I am worried about my exgirlfriend possibly wanting to hook up with my best friend. There aren't really any direct signs of it happening.

One day over Thanksgiving break while I was in my hometown my ex-girlfriend's sister had randomly texted my best friend not knowing who it was. (one of those immature texting random people to see if they get a reply). My friend had come to me about it showing me the number, and then I had figured out who it was. They started figuring out slowly that it was my best friend. Once they had asked him if he knew me, he had done the right thing and said, "nope." and as far as I know stopped texting them. While they were asking him this, my ex had actually ended up calling his number, and he asked me who it was. I had told him who it was, and he just ignored it. He then told me, "i dont want to get in the middle of any of this. i know it's really complicated."

Some background on this situation might help.

My best friend has been sleeping around a lot lately with girls. He knows it is something that he shouldn't be doing, but he still does it and shows no real signs of imporvment. He knows that I have been having a hard time with this break up for the last almost 2 years. When I had shown him a picture of her once he had just said, "wow now i can see why you always hook up with her." This made me feel really uneasy.

He is going to be moving back to the hometown where he and I are both from, and where she is currently at. I on the other hand, am not. This situation has made me feel very uneasy, because I have had my old friends in the past betray me, and go off with her once before. I just don't think I could handle my best friend doing this.

I had told him about this feeling, he told me to put my mind at ease, that he has no idea who she is or really what she looks like. I had told him how it would make me feel if it happens he always just told me he understood.
He has always been a great friend to me, and I hate to break this trust over something very stupid. I don't know how to calm my mind. Any advice would be great.

I think there are two issues here that you have tangled together.

First - This girl is your ex – going on 2 years now. Who she decides to hook-up with now is none of your business.

Second – You cannot control your best friend. If your best friend is trustworthy, he'll keep true to his words and not "get in the middle of this".

I think you are hanging on to a wish… You wish this girl was yours again, or at least not with anyone else. You're also jealous of your best friend's social ability, and wish you had the same skills (to get her back, maybe?).

If you want to calm your mind, you need to let go of those wishes. You already acknowledged there are no real signs of something between those two. Accept the reality in front of you, and let go of the worry.

Being that you already expressed your concerns to your friend about this situation and he stated he won't betray you there's nothing for to do but take his word. If he is your true friend he won't even go near your ex because he values your friendship.