Well here's the thing... I've been dating this girl for almost a year and a half, and we both love each other. This could be said to be a long distance relationship, but not that much we are only separated by 1 hour of driving. Well, the thing is, I have been having some issues with her because of the fact that she is talking to her ex-boyfriend. I trust her a lot, she's proved to me that she deserves my trust, but I don't trust her ex, since I know he still has feelings for her. Everything started a few days ago, and she even told me that she was going to send him a message from Facebook because his grandma just passed away. She asked if I was OK with that, and though I told her I did not like that idea that much, but if it was for that, that it was OK. So she sent him the message and she told me when she did it. Well, the thing is, since that first message, they've talking a lot these past 2 days, and I got kind of afraid because I knew he still likes her. I told my girlfriend that I did not like that idea at all, that it should not be done. I made sure to tell my girlfriend that this bothered me, and she understands. The reason she told me she is talking to him is for them to work things out and be friend, since they go to the same school and it is annoying to avoid him all the time. I kind of understand her reasons, but still this is too much for me. Should I trust her with her decision or just follow my instinct and say something about it?

Oh, extra information... they broke up 2 years ago and we been dating almost 2 years, I don't know if that changes the whole thing.. im just afraid she will fall for him again, and my behavior is not helping

Then stop your behavior. There was nothing wrong with her sending condolences to him for the death of his grandmother and she asked you about it. You either trust her or you don't. If you do, leave it alone. If you keep bugging her about this guy she is going to get tired of it.
If you don't trust her, leave her alone.
How do you know her ex still likes her?

Yeah, I know there's nothing wrong with sending condolences to people, but this guy just took advantage of than and now they have been talking nonstop for the past few days. I know this guy still likes her because he told her that she misses her and that she means a lot to her.

So. That does not mean she wants him. You either trust her or you don't.
We females don't fall for a guy just because they may like us. Just because he misses her, it does not mean she will leave you for him.

I know, and this type of things don't usually bother me, but since this is her EX I don't know how to react, I am scared that she falls for him again. I do trust her, but I just don't trust him you know?

Well just don't harp on her about it. You either have her or you don't.

Yeah, you probably right, the more I think about it, the more I worry for nothing. I should only worry about her, and that she's with me and I love her.