I don`t know if that will help but: lets see:
Why would he really leave you? Maybe if you give yourself the answer to your fear - i mean - let your fear speak up so that you get to be conscious, aware of this:

If you think that he is going to forsake you when he is hanging out with friends, or that he doesn`t love you, then - what reasons there can be?

See if they are rooted in you or in him. Like:
"My fear is that he will forsake me because i am crazy!"
Or: "My fear is that he will stop loving me because he is a nasty person and he never really showed enough love!"

Because there might sit a bug somewhere in your thinking system. I agree with Martina that our black white thinking is a problem but there is a reason that creates it.

Otherwise i agree that in ANY relationship giving a second though about a situation can bring you to a totally different feeling about it!

sorry for this pain. i know what it feels like. this crazy swing back and forth. But it is possible to balance it .Its impossible to completely rely on another. We need to be conscious of our own strength. It is there. We just need to find it again.