Don’t get me wrong; he doesn’t want to. That’s incest-- but he does want someone like his mother, functionally speaking.
His mother cooked his favorite foods, cleaned his room when it was completely F’ed, nursed him back to health when he got the flu, and helped finish that science project the night before it was due. She picked matter out of his eyes and ears, told him he could be President, bought him that cereal he was never going to finish, and wasted half a bottle of Shout trying to fade the shit streaks out of his underwear (fail).
He’s a man now, but he hasn’t outgrown his need for a nurturing female presence. He needs someone like Mom… albeit with a twist.
The mother/whore complex-- “lady in the streets, freak in the sheets” is the popular colloquialism-- is generally believed to refer a man’s need for his wife to assume a maternal role-- attending to his needs without violating his pride-- while also transforming nightly into a succubus (pun intended) whose position-of-choice requires a stunt rig.
Most men want a woman who can comfortably navigate these two worlds, but if you can’t then it’s okay! The original Freudian concept of mother/whore described a man who relied on his “main” or “wifey” to act as a surrogate mother; because this didn’t jive with his sexual urges-- again, boning your mom is gross-- he would literally explode his base desires upon lesser women (jump-offs, scalawags, chickenheads, skanks, skeezers, hoes, tricks, trick bitches, side orders, freaks, cum-buckets, and “Jolene” [good song]).
Chances are your man won’t cheat on you if you can fill both roles. If he does cheat then it’s probably because you were either the maid who couldn’t swing from a chandelier or the prostitute who couldn’t vacuum or fold. Some men, however, consider the two roles to be mutually exclusive; in this case you’ll always have a “silent partner” providing help, whether you want it or not.