I am the last person to be able to answer this question right now. It's really hard... I let go of Gerhard because I had to. I let go because I had to make peace with the fact that he wasn't coming back and that I wasn't going to have my happy ending with him, even if he was the only one I ever saw it with, at the time. I had to let go. It was hard, but I almost did it. I had more trouble letting go in my heart than anything else. I had moved on with my life, I was seeing other people, avoiding contacting him and avoiding talking about him. It helped a lot. Then... he came back. But that's a whole different blog post on it's own.
I guess it all depends on how you feel, whilst still being realistic about it. I mean you can love him but if he's treating you like shit and he's so much bad news - let go!! But hey, that's just an example.
What do you think? Please help?