What do I do about this

well me and my girlfriend broke up and one of my other friends were there for mr after and I thought she was just amazing and has actually always been there for me and ive been there for her but even after all that she just goes out and finds someone to date and what else I found out is she basically says the same things to alot of people

things that I think would be used more cautiously instead of just thrown out so I just wanna know what can I do about all this and now its worse cause I found out that she is dating one of my other friends

If ur friend has a Facebook then u can c if he is in a relationship and if it doesn't say who then u can get one to him and ask him

Be her friend for a while, especially til when they break up. Then continue to be her friend... be there for her and just be closer friends, then it's easier to find out who she likes and/or how she feels about you.