Confusing Relationship/Story

I work in a company and am good friends with X
Everyday we used to go for Lunch together and a girl (Y) used to meet us for lunch.
I didnt think anything of it.

A few ago, X left the country for some work.
During this time, Y and I got close.
We met up for drinks once and totally hit it off
She opens up and says that she doesnt believe in relationships
When we're casually talking, we talk about X and she says that yes, X is a person she would probably consider dating.
X calls her when we were there and i joke to him that she would like to date him
I dropped her back home and we had a hug, a really long lingering hug
I didnt do anything about it

Im very focussed on work and dont really pay that much attention to women. i dont have flings. I like things to have a purpose.
A week goes by and we're texting everyday.
Im a little flirtatious, she is not.
One day i turn up at her doorstep with flowers and all
and she is totally smitten
She suddenly says that we need to talk
I'm like sure

We go out
She sits me down and says that she's seeing someone
and that i should stop flirting with her
I apologise saying, i didnt really mean anything by it
and that i didnt know she was seeing someone
She describes her relationship

The guy in question doesnt want anyone to know that they are in a relationship
Its all hush hush.
This is a red flag for me and i go on a rant
On how she is awesome and she needs someone who has passion
and tell her sweet stuff on how she deserves to be treated

she gets emotional
she says, that after our first night our she wanted to kiss me
i say i wanted to too

meanwhile, i figure out by matching character traits that her boyfriend is X
I decide that i want to backoff because this is too complicated then
Im annoyed that X kept this from me

The next morning, she comes over for a quick breakfast cause she feels bad about putting me down
We hook up
Over the next few weeks, she tells me all about herself
we go on drives in the middle of the night
she is brutally honest about her background
how shes gone through so much
Im impressed and fall for her

She tells me about her relationship with X
She tells me how they never spend time together
She tells me how they meet once a week at most (Other than our run-ins for lunch)
She tells me how she told him she loves him and he didnt say it back
She tells me how she keeps fighting with him because she doesnt want it to be a secret

I tell her i love her
She tells me that she loves me

This goes on for a while
we're totally honest with each other
X comes back from his trip

I meet him the first day at work
and i tell him that he shouldve told me
if he had told me i wouldnt have hit on her/flirted with her in the first place
he denies the existence of relationship

A week goes by
Y and I decide to not stay in touch
It was a mistake, they are a couple, im nowhere in the picture
I accept it

I catchup with a friend (Z) for dinner
Im a little upset and want to tell her the story (minus the personal details)
She starts crying
She says that until a month ago, she was dating X
She ended it when she found out he was also dating another girl (P)

As it turns out
X was dating P
then X started dating Z
then X started dating Y

I dont really know all the details of their relationship
I want to call X and tell him
At that time, X messages P telling her that im a dumbass for assuming X and Y are dating and he insists that nothing is going on with him and Y
I call Y and tell her we need to talk

I go home first
Talk to my sister and ask if i should tell Y the whole story
I want to do so, but im a little emotional right now
She says that i should
I go over to her place and tell her the whole story

Y is weeping
P sends me chat screenshots that Y shares with X
Lots of drama
Y says that she cant deal with this anymore
Y wants to leave the country for a while
Y goes abroad
I'm supportive during this
I told this story to a friend of mine about how upset she was
and he/she replied asking why she was upset, since she also did technically cheat on him with me.
Y sees this message

She is abroad and she talks to me every night
She talks to X every night as well
We talk about the possibility of us dating
she talks about how she doesnt want relationships anymore
She then opens up and says that its weird
All her friends just came to know about X
and she cant just go and tell them suddenly that shes dating Xs really close friend
She mentions that she wants to give X another shot
They arent dating, but she wants to keep it open and see where it goes
cause she feels guilty cause she technically did cheat on him as well, its just that he managed to get caught
During one of our conversations
I say that its not healthy to talk to me and him every night
she needs some alone time to heal and talking to me/him would be counter productive
I also say that he would probably be uncomfortable with me talking to her
and i dont think its a good idea for her to talk to him
She says then shes not going to talk to me
Im a bit hurt and i put down the phone
She tells me that shes tired of people telling her what to do and what not to do
I back off

A week later i talk to her
we start talking again
we become super close again
Then she tells me that she talked to X a day before and they want to give it another shot
Im upset, and i hang up
She calls back and we have a fight
she says that she lied, she just said that to push me away because we were getting close
im upset because she had a choice and she willingly hurt me.
We stop talking

We work in partner companies
X goes abroad for work (faking with the company that he's doing some work whereas his actual goal is to win her back)
So there is an opportunity abroad
I go abroad as well, but to a different city (X&Y are in the same city)
I talk to Y only for work, keep it formal
but inside its eating me alive
So one day i make a decision
I call her and tell her i want to talk
Then i tell her
that i it hurt a lot that she was willing to throw me under the bus that easily
i want to vent, and i tell her that im venting
Then i tell her, that we can be friends
because in all of this i've realised that she is quite lonely,
more than a lover, she needs a friend
it still hurts me that im the one shes completely honest to
She cant be that honest with X
But still she's dating X
Its a brutal hit to my self confidence
What does he have that shes with him inspite of everything
and me, inspite of being so nice to her and everything, cannot get her

Its the hardest thing i've had to do (atleast it feels that way)
but i do it
im supportive of her
She tells me how shes back together (not fully, they're dating, but shes not sure about anything) with X
I support her, im a friend.
One of her only close close friends

I havent told her, but i still have a lot of strong feelings for her.
But i dont trust her like i used to
From my conversations with her
it sounds like shes given him another chance and is just waiting for him to **** up so she can leave him
i cant be sure about that though.
But she is really fragile
She takes really emotional stupid decisions
And i really really care about her

And here i am
The guy who voluntarily entered the friendzone

In my opinion, i made the right call. Its hard for me and a piece of me dies every night
But shes happier and happier every time we talk
She talks to me much more than the 'boyfriend' X

Any advice on what i did wrong?
What i could have done differently?
What i should do?
Should i try to pursue her?

Would appreciate the opinion of someone of the opposite sex.

Dude, you need to take those rose colored glasses off and see she was using you the whole time. She knew X was dating someone else and she was the other woman...that is why they kept it quiet. She was willing to sacrifice her dignity to have him. She kept you at a bay, by telling you she didn't believe in relationships....that was a lie, she never did want a relationship with YOU. She wasn't getting what she needed from X, she was in emotional turmoil over her secret relationship with him, she needed a rebound to make herself feel better. You were her revenge on X for having this other girl....

Your buddy must be some hot stuff for these women to throw themselves at him. Why they take it? Because he's a player, he oozes masculinity, confidence and is a challenge. He is such a hot prize they shamelessly want him bad and don't care what they have to do to be with him.

This girl Y, is using you to boost her self confidence.....stop being a damn doormat, letting her walk all over you. Kick her to the curb...you can't rescue her from X, never ever. Walk away from it all.