Im sorry, I have been there. I hope you will find a way to not feel so much pain, I wish you well!

I think the only way is cut all contacts if its possible, it helped me. if its your T you can talk to him about it, if its someone another and you are pretty sure you cant be with him, do what I said before. Yes its hard but its the only way to stop it.
You feel like in hell now with or without him. I know how it is. Leaving this person helped me, it was really hard and painful but now Im free of those feelings.