You both need individual and couples counseling. If she won’t go, you go on your own and work on yourself. It’s pretty fucked up you’ve been thinking about another person for so much of your relationship. The way you feel about Diane is most likely just a fantasy because you don’t feel happy. Rather than focusing on the real issues and working in improving them, you have developed a fantasy about Diane and think your life would be better with her and in all honesty you’d probably still not be happy.