Ok it goes like this... I used to date this girl for a long time a while back, but never forgot about her. Well she comes to my house and we both agree how we feel about each other. That she missed me just as much as I missed her. She wanted to have sex with me,but I told her I didn't want to have sex unless we were acually together, but I gave in anyway. Well for about 2 weeks everything is going fine. All of a sudden she won't answer her phone, doesn't call me back, and won't reply to my e-mails. I only call her once every day or two so it couldn't be that she needs space. She comes by to get my nephew several times to take him to the waterpark and baseball games with her nephew and doesn't even come inside to say hi. Then she came by again to drop of my nephews clothes and we made eye contact, but she just goes to her car and leaves without a word. Do you think she is back with her ex or another guy? Why is she avioding me? What should I do?

Have you taken into consideration that she might be pregnant or at least late for her period and afraid to tell you? Now, I'm not saying this is the case, I'm just saying it might be possible.

And why is she coming to get your nephew? That wasn't explained.

How often are you trying to make contact with her?

If you are trying to make contact with her multiple times a day, then give her some space. Most women I've ever met or dated wanted to be with a man who was secure with themselves. If you show her that you have other things to do besides chase her, then there is a chance that her interest in you will grow. Take some time to avoid making contact with her...

It's hard to say if she is seeing someone else... if you want to know, give her some time and then just ask... the worst she can say in this case is yes.

You have already done everything you could, she cut off contact with you it's time you cut off contact with her. You will be better off as the mind games will finally come to an end

She used you for sex, and got what she wanted, and that's the end of that story, unless she is indeed pregnant, and that you'll know about soon enough. Leave her alone, she doesn't want to talk to you.

Sounds to me like very possibly she, in her mind, compromised (illogically as it may be)
With you that okay you don't want a one night stand sooooo she would put on a charade for a while like you were back together and then dump you like a bad habit.
Don't fall for it again. She isn't going to suddenly have a change of heart, fall back in love with you and come running back.