I am an overly anxious person in general. Just to put that out there.
In my last two relationships before the one I am in now, I was cheated on. In some cases, multiple times. In one of those relationships I made the attempt to work things out even after I found out that they cheated on me. That ended up into being an extra 8 months of me not being able to trust them, and eventually I had to end that relationship. Both of these unhealthy relationships were in a row. Right after they occurred I met my current girlfriend and we have been dating for a year. At first I wasn't too jealous but I see myself becoming very jealous.
A lot of times when I come home to our apartment, I am afraid to find her having sex with someone else. The problem with this is, she has not given me any reason to believe that she is being unfaithful whatsoever. One of our new friends, we both think, has a crush on my girlfriend. I am very jealous of when they hang out together. Even though underneath it all I feel that my girlfriend wouldn't cheat on me, I still have these crazy fantasies.
Is it because I was cheated on before? Am I just really insecure? Can someone help me work through this? I have brought it up to my girlfriend, but I feel so bad about it.
live your life with arms wide open
A small dose of jealousy may be healthy, but too much of it will destroy any relationship. Actually, it can even lead the other person to cheat on you.
Did you also experience jealousy in our previous relationships? Do you also feel jealous in other areas of your life: with friends, in your family, in your work, etc?
I think this is something you need to work upon, but I really don't know how you should approach it. Maybe it's a side-effect of your low self-esteem. Or maybe you take life too seriously and are unable to play a little.
Look at your daily routine. Do you think you could insert some more light activities in which amusement, fun or whatever would be a major element? Have you ever thought about performing (playing in a theater) or learning to perform? You would deal with your emotions in a safe environment and in a certain way you would make them less dangerous and disruptive.
I think Pendulum makes some good points. A little bit of jealousy is normal. I actually believe jealousy is an instinct and it helps alert us when something is not right. In your case, I think your past experiences being cheated on has made you a little paranoid and this is totally understandable! When you told your gf that you are worried/jealous, was she understanding? Perhaps if she knows where you come from with relationships she can be a little understanding of it. However, I think you do need to work on this. I agree with Pendulum that you may need to relax and enjoy the good. Don't worry about the future. If she cheats on you, then you will find out she is not the one for you! It may hurt and really feel horrible, but it means she does not deserve you and you can move on and find someone who does. We are not all prone to cheating and you will find someone who will be 100% faithful to you!