Dazed, I totally agree with Fuffy. Depressives often use the pedestal approach. New woman is on the pedestal, he's obsessed, the sun is shining, all is perfect in the world and D is at bay. Until one day they have a fight or she says or does something which irritates him, and makes him angry, he becomes cold & distant and SHE is the one facing fallout. So he will look elsewhere for someone new to put on the pedestal.
Your marriage is certainly not the cause of his D. It's easy to blame your marriage to justify the cheating. He is fooling himself to ease his conscience.
My exdf blamed me for driving him away. Into the arms of a married co-worker. What a compliment to her!! (SARCASM) "I'm only with you because my ex fiancé is a %%*+# and she drove me towards you!!" Words every girl wants to hear!!
Hugs to you Dazed.