Rae,
He did this because he wants a mommy, she does not judge him, does not complain, she is happy to have doormat written across her forehead, why should he put up with someone who has self-esteem and will call him out on his crap when he can take the easy road.
I know it hurts, my wife cheated on me for a long time, when I finally caught on and called her out she just moved out, she was going to milk it for as long as she could so she could divert money away from our joint accounts.
Did I want to burn his house down with them asleep in it, hell yeah I did, but to what end, I moped around for awhile, then I got into counseling, pulled myself together, started dating again, and married a wonderful woman and now we have two great kids.
I think you dodged a huge bullet, do not think of this as wasted time, think of it as a life lesson.
If you need to talk or you just want to talk about how men are pigs, well I will be glad to listen.
Big hugs to you,
Bill