Re: Am I crazy or is something going on
You have every right to be concerned. Him insulting you that you are crazy is called gas lighting around here and DARVO as well. It is an emotional affair pretty much, maybe has turned physical by now, but you don't have proof.
You two need to talk and seek counseling. The neighbor needs to go. If she is married, her husband needs to know what is going on behind his back. If she is single, she is after your husband.
Your husband is weak. As soon as he left you that summer ago, he brought another woman into the mix. He needs to end one relationship before starting another. He doesn't want to feel alone and automatically changes partners from one day to the next pretty much. Where is his love for his wife, even if separated? My guess is that you thought you were on a cooling off period and not separating to seek others right?
You have many issues to discuss, hopefully with a good counselor.
Good things come to those who wait...greater things come to those who get off their a$$ and do anything to make it happen.