“God wants me to be happy! God gave us this [illicit] love for each other, therefore we’re meant to be!”
“I met x because God wanted me to meet him/her.”
“God sent me (affair partner’s name).”
I’ll keep this short and sweet:
If God is telling you to be with someone else’s spouse, that’s not God. You’d think that’d be a no-brainer, but sadly we know too well how difficult of a concept it is for some to grasp. God will never call you to commit adultery. He does not call you to sin. He calls you to holiness, repentance and life eternal with Him. Eternal life is not waiting for you in someone else’s marital bed.