He's not emotionally invested in his marriages. Time and again in his auto-bio, he gets married, they hit a rough patch and he magically finds the girl he's supposed
to be in love with.
The first time, he married the girl because he had knocked her up. After leaving the Army moving back to the States & going to college, things got rough between them. That's when he met, & started flirting with, the women's assistant VB coach (named Tammy, I think). They started having an affair, his wife found out, they got divorced, & he married Tammy.
Then, just before TUF 1, Randy realized Tammy nag & was looking for a way out. Magically, as he was in Vegas shooting TUF, he met Kim & started an affair with her. Tammy found out, they got divorced, & he married Kim.
I'd be willing to put money down that Randy & Kim hit a rough patch & Randy started seeing someone on the side.