Hey,
So here is the story.
We have known each other since January 09 and dated up until that September, when I left for mental reasons. She used to get angry at me all the time for every little thing and my anger at it was getting way out of control so I had to leave. I then dated someone else for a week and didn't really have anything important with them.
After a few months I started thinking about how badly I missed her and how I wish I just tried working though my anger instead of giving up so I emailed her apoligizing (she wouldn't answer a call). I told her how I felt and how sorry I was about leaving her and that it was a mistake. We talked over email for that entire day and then finally got to see each other again. When I saw her I immediately knew I wanted to be back together with her and she seemed the same way. We finished hanging out that night and went to her car and made out for about an hour and we said that we loved each other for the first time since the break up.
After that I started seeing her regularly and we showed plenty of affection towards each other and had a regular sex life, too. She would tell me she loves me but always said no If I asked her to date me because of what I did (I understand it was low). I got it then, but now it has been 8 months since I came back into her life and she has been losing more and more interest in me, to the point that she won't kiss me on the lips anymore.
All she has been doing on a day to day basis lately has been going to other guys houses and hanging out there and comes home too tired to even put any effort towards me.
I have tried to stop being jealous (one of our biggest problems) and I am not showing any of it towards her because I know it will just push her away but I really don't know what to do anymore. I love her with all my heart and I want to marry her someday but I can't figure out what to do in the situation I am in. I love her affection and miss it so much.

Lets see, you left because she had ways you couldn't deal with, so you got back with her and it seems you can't deal with what she is doing now.

While affection, and attention is a good thing to have, being able to honestly express yourselves to each other is what will tell you if she is willing to work with you, and RESOLVE your issues to the benefit of you both. No matter how strong your feeling for her are, she has to be ready willing and able to work with you so you must communicate your feelings to her, and she has to do the same.

Jealousy is another form of insecurity, which is rooted in FEAR, and I don't know if its more affection, that you want, or if you are needy in your wants, but I do know if your waiting for her to come home, and show you attention, then I also think you have nothing else in your life that balances your time, and attention other than her, and that's when you become too dependent on a partner, and that will make for a very unhealthy relationship, and a breeding ground for very negative thoughts, and actions.

Sometimes we all get so carried away by our own needs we miss the facts, or fail to understand why we feel as we do, and instead of communicating, we assume, and presume, instead of talking, and listening. That's my advice, examine your feelings to see if they are realistic, or a bit needy of you, so you can make adjustments, and then talk to your partner, and see if she is willing to make adjustments also.

Being with friends has its good, and can be bad when overdone, but by the same token, if you have no friends, then YOU need to make some adjustments, and correct that. Its unwise to depend on someone else attentions to make you happy, as you should already be happy, and be sharing it.

That's obviously not happening, and obviously, you are not communicating with your partner, in a positive way.

As I've found out through my recent dilemma (you can find my post). You can never force anyone to do anything, especially with love. These things must come easy whether it's from you or her. When someone you care about does not return that affection, it hurts. Trust me I know. Relationships are a 50/50 deal. Don't give your all to someone that doesn't want to give their all to you.

As your post title says "(kind of) girlfriend" is that really what you want? Cause trust me having a REAL girlfriend who shares their affection is better to have. So tell you what. Pick yourself up and start thinking about you. It's what I had to do. Also, don't beat yourself up over what might be/will be. I don't know if I'll ever get back with my ex and I was with her for a long time. It sucks yeah but life moves on. If it's meant to be it'll happen otherwise it won't.