Steph is addicted to the thrill and high of cheating and lying. She cannot help it. She probably had an affair with the husband behind the MC back before they married. And now she has an affair with the MC behind the Husband back. The MC and the Husband are basically Eskimo brothers at this point. She came so hard because she thought her husband could catch her at any moment if you do not pull off. And probably she came again with her husband thinking how their was another man inside her moments ago. The MC falling for her is like a high school boy falling for a pornstar.