"you didn't fulfill his needs or feels he needs to explore a new R in order to grow.
I gotta disagree with this interpetation. Lots of times it's about the WAS being depressed and looking to self-medicate their depression with the "drug" of infatuation with someone new, EVEN WHEN they had a perfectly good, loving spouse at home.
No relationship is perfect, but I've seen lots of pretty darned good relationships fall apart due to MLC. MLC is about a fear of aging, a fear of death and dying, and a fear of "missing out" on something. It's important that the LBS take a good look at themselves and fix what they can, but honestly, it riles me up when people say the WAS wouldn't have cheated if they'd been happy at home. My ex and I had an excellent intellectual and sexual relationship, I was loving and kind, we had a great family, and we were the couple most people thought were rock solid. But he had issues around fidelity that were HIS issues, compounded by a mood disorder, compounded by MLC and my inability to morph into a 30 year old Asian chick. I could have twisted myself into a pretzel and he still would have left. I have peace in my heart that I gave everything I could to my marriage.