I don't think I'd forgive them unless they apologise. This is my new opinion, if I was asked this few months ago I'd have said that I'd forgive them even without apologising.
Now things are different and I think I got tougher and solid, I wont forgive without apologising any more. It doesn't worth it.
From what I have seen in life, it is not easy to go on after someone has cheated on you, or have neglected the friendship between me and him/her. Still it all depends on how we live and what we go through.
Few months ago I'd say, I'll forgive. Now I wont.