Spinneret (Renew Your Vows)

Ah, this one is quite popular. In the universe this Mary Jane comes from, Civil War and subsequently One More Day never happened. So she's still happily married to Peter Parker, and they have a daughter together named Annie.

Using technology acquired from a supervillain called the Regent that her husband defeated, this Mary Jane can use Spider-Man's powers at half their full strength, allowing her to become a superheroine named Spinneret and fight alongside him.

As this MJ is still married to Peter, she won't immediately be willing to 'cheat' on him with you. Of course, you can change that if you want.