My boyfriend has his ex in his close circle of friends

Hello,
I specifically need to ask the men out there, what your opinion would be about this scenario.
I'm dating this guy and we are planning to take things forward, possibly into marriage.

We had hit it off VERY well at the starting of our conversation itself, and are still going strong.
I'm yet to meet his friends (which is going to happen soon, reason why I'm a bit excited/jittery) because, I have figured out that his ex-gf also belongs to the very same friend group.

Now, I had easily figured out that this ONE girl in his friend group was his ex, from social media....from the way they posed in their yester-years' photos, that chemistry....it was pretty evident. So one day on our date i just asked him about it. He said before dating, they were good friends belonging to that same group in college. But others seemed to have had noticed an undercurrent of chemistry in them and suggested "you both get along so well...u shud date", and they too thought, why not !
So they dated, they loved , they fought...and then they realised that they were SO LESS compatible, that their quarrels were dominating the otherwise good friendship they had .
So like wise kids they broke up. But needless to stay, they still stayed friends as they had the same friend group.

Now, I have NO ISSUE with anybody's past.
I myself have had 4 ex-s in the past...I'm even friends with a couple of them....but then, I am not in a CLOSE friend circle with any of them. I don't have my college-group re-union every month where any of my ex comes in, nor do i go on weekend trips with my buddies where my ex is a part.
I understand, for them, it's tricky coz just because these two broke up, it won't be fair to expect one of them to go out of that strong friend group and establish a new social circle. NOT AT ALL. I totally get it.

But, having said that, I still can't deny the fact that it keeps eating into my mind every now and then that these two keep catching up (probably in group, i hope NOT one-on-one) for sunday brunch/ friday nights/ friends' wedding parties/ one day trips. After all, I am nothing but a human of normal flesh and blood. And me presently staying out of the city for a month for work is driving me nuts (they all stay in same city)

My question is: What should I do?
I do not wish to take this up on phone/ snapchat. I wish to meet him and discuss about my concerns...which, won't happen before another month given my work pressure.

I do NOT wish to scare him away by coming across as a possessive GF (read soon-to-be fiancee)

I AM cool with his ex catching up in groups...heck I even want to meet her...I cant deny I'm curious to know her. But....I still would secretly wish HE doesn't go on weekend trip with that friend circle, if any time I'm not able to join them for work, but she is going.

Basically I'm okay with him catching up with her IN GROUP.
I'm also okay with them going for lunch/dinner parties IN GROUP even if I'm not there.
I'm okay with her coming to trips with us ONLY when I'm there.
I'm also okay with him going on trips with his friends WITHOUT me if I'm busy with my work any time....but I'll be very very insecure if she is there on such a trip, in my absence

Now, guys please do tell me......how am I to deal with this scenario?
First of all, do u feel this is a normal situation?
How do I convey this to him without spoiling whats between us?

He perceives me as a VERY rational, chilled-out, logical woman....who he feels is more matured and humorous than him despite being younger than him by 2 years. The last thing on earth that I would want is to dampen THAT feeling of his about myself in any way.

So please tell me....how much paranoid I'm allowed to be about this situation...and how do I talk to him about this.
Or, should I back out from the whole relation just because this is a major bothering that'll keep bugging me even through my marriage?