What Should I Do?

I started a long distance relationship a few years ago and then it got to the point where we met and we kept seeing each other then times were starting to get bad as we were both busy with the other wanted to see and decided to end it, this happend recently.

During the course of my relationship my partner came into contact with my next door neighbour and started talking to each other. I didnt think much of it untill one day she told me that he was sending her dirty text messages. I was so furious that I wanted to hurt him then he told me it was just a joke but I felt even more angry that he would do that to my partner.

Well I was talking to her on the phone a few days ago and she tells me when we broke up she imediatly started seeing my next door neighbour even though he was a really bad friend to me and it would still be a long distance relationship for her.

Right now I am so depressed because I can't be in my house knowing that they could both be next door and I just want to hurt him soo much because I know he is doing it to get back at me (Not paranoid feelings) and I honestly don't mind that she sees other guys, just not him cause I know he is going to hurt her!!

Any ideas on what I could do? It would really help as I am getting stressed out too easily over this.

Leave them be. She chose to approach your neighbour, he chose to get involved. You stressing over them because you fear he'll 'hurt her' is silly and unnecessary. The proximity thing will bother you, yes, but this is a hurdle you'll just have to work your way through. Forget about it, move on, be happy.

^ I agree with both the posts above.
If he hurts her it's for her to deal with. You shouldn't be worried about her especially not after she chose to be with him.
Give it time.