
Wow. I'm really sorry, that sucks. Dr. James Dobson (Focus on the Family) wrote a book called Love Must Be Strong. It encourages one to bring the other person into a place where they have to make a decision - they can't just keep screwing around. Dobson is a Christian and the book is written from that perspective, but I think no matter your beliefs that it would be a worthwhile read...though it has been a year or so since I read it.
Hang in there...while sometimes it doesn't feel like it, there will be light at the end of the tunnel.
Dave