What should i do about my ex gf?

So we broke up recently because her feelings changed. ( i accept that and have no problem with ) One of the reasons she gave me to brake up with me was because of another guy she was hanging out with but apparently nothing happened while we were together. During the time we were together i never saw him as a threat because she plainly told me he was not her type physically.

Now we are apparently still friends hanging out a fair bit and i still know for a fact she doesn't like this other guy and it feels like she is using me by hanging out with me to get the other guy she broke up with me for away from her now. Recently Ive also found out she likes another guy and has hooked up with him ( she teaches him a music instrument lol ) and she wants to become a teacher but that's another story that i personally find funny that she likes someone she teaches something to.

Now this guy she likes wont commit to her but again she still is hanging out with me and again i feel like its because she is trying to make the other guy commit to her and make it look like shes a in demand kind of girl..

Anyone have opinions in what i should do about her? It does bother me to think she is using me and she isn't one of those types of people you can ask up front if she is using me.

Thanks for reading and replying