tips on how to start to tell her I love her, tips on how to find out if she likes me as well. I’ll try anything.
Here's a tip: Stop talking to her altogether so that you get over her for goodness sakes. You've waste two years of dating time not looking for your own girlfriend because you are crushing on someone who has a boyfriend. Even if she's no longer with him now, she's clearly not interested in you or she would have made it known that she is single.
I can't believe the people who are encouraging you to go after someone who is already taken. How would you ever be able to trust her if you were actually able to take her away from someone else. If you can do that, that should tell you that she doesn't have good romantic relationship boundaries and someone who doesn't have those, often has a hard time staying loyal.
End your contact with her so you can squelch your crush and therefore be ready to find your OWN girl. That one is taken or not interested in anything romantic with you.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion