How does he treat your wife? If he is treating her well it might just be a case of the 2 of you just aren't meant to get along. There isn't anything saying that you have to be friends with the boyfriend. Some people just don't mesh well.
Your wife is responsible for her relationship with you though and just because she has something shiny and new in her life doesn't mean that she gets to neglect you. She should be putting some effort in to carving out time to do special things with you that the both of you enjoy together. As for how long it takes to see the positives that can vary from person to person. Are there things that she enjoys doing that you have no interest in? Is there something that you would like to do but have been feeling guilty about asking for the time to do it?
It sounds to me like you and your wife need to work on being connected again. Sex shouldn't just happen out of "fairness" it should happen because you both want it to happen. Plus relationships have their ebbs and flows, if you're both willing to put in the time to reconnect and find why you fell in love in the first place hopefully you'll find the spark again.
Everything will be ok in the end. If it's not ok it's not the end.