I am really upset because I really hate the guy and he is still hitting on her and she just thinks that they are just friends and when I found out she said that it is not true but a friend gave me the conversation and it had I miss you and stuff. Her answer was I was always close to him and what we are saying now and stuff are non of your concern and it's my personal life.. We all have secrets and personal information

Im going through the same thing buddy.
I left my boyfriend because he was still talking to his ex.

If your ex has NO kids with this guy, there is no excuse for these two to be talking.
If she loved you, she would stop. Point blank period!

Yeah, it is her life and she's allowed to keep personal stuff from you sometimes, but this is not something that she should be keeping secretive. No one wants their partner to be talking to an ex if all the ex is saying is "i miss you".
And her texting him through all of that just shows she might still has feelings for him and it is really disrespectful to you.
You should sit her down and tell her exactly how you feel, tell her you don't appreciate her talking to her ex since he seems to not be over her. And if she respects you and cares for you she will stop. If she doesn't then is she really worth it? Do you think you'll eventually have trust issues? Is there a chance she could cheat? Just sit her down and talk, try to be the bigger and stronger person.

Talaniman Rule - Leave people with exes in their lives alone.

Who needs this drama and confusion? To many nice ones that HATE their exes to be stuck on one that doesn't.

Is time to move on, if you have talked to her about it, and she doesn't respect your feelings, then she probably doesn't respect anything else. Break up with her, if she comes back clean then she really wanted to be with you, it seems like you are being put second.