Re my WAP not being MLC because of the time frame/affair etc - is MLC on a timeline re the relationship? Yes, what you say is possible - my WAP dies NOT have a blemish free history.
No, there's no time prerequisite on MLC, BUT - I'm just pointing out that it's relatively uncommon for this to occur so early in a relationship without there being some other underlying pathology. And if, as you say, his past is not "blemish free" - you may need to look a little more closely at that past and see if this is just a predictable repetition of an old pattern.
I've seen two patterns on this board when a marriage (or serious relationship) falls apart so early:
1) The spouse was cheating all along. Many times a marriage that falls apart in the first year or two, it turns out the spouse was already cheating BEFORE the wedding! You may think it is impossible but just like drug addicts, they can be very adept at hiding things.
or 2) The WAS has a history of sudden turnabouts like this. Many posters here thought somehow THEY would be different from the previous three wives left without child support, and are surprised when their spouse walks away that he treats THEIR children with the same disregard he did his children from his previous marriages.
Please read that book on The Sociopath Next Door. My sister was married to one. He seemed like the perfect loving husband, then walked out one day. Turns out he would play kissy face/"I love you baby" at the door when getting picked up for work, then complain about my sister all the way to work to his co-worker. She had no idea. He's had two marriages since and 2 more children besides my niece and has abandoned them all with the same abruptness. Sociopaths can be very very good at playing a part - until they no longer want to play it.
What do you really know about his past relationships? Do you only have HIS version, or have you ever spoken to any of his previous partners? Did he leave someone to be with you?