I don't see any reason for Nicole to need to kiss or have sex with anyone for her and the MC to break up, it could simply boil down to MC telling Nicole that he really likes where he is now and that working for the hotel is what he wants to do, Nicole is obviously upset and tells him that she doesn't want to move there and up route her life and lose her position, the career she has worked for, they break up, both sad their relationship is now over but understanding of the others choice, MC offers to continue to pay his portion of the mortgage dept, end of Nicoles route she is no longer seen in the game.
You don't need drama and cheating as a justification to end a relationship the game, they both care about each other so I don't see why it can't be amicable with Nicole seeing how happy the MC is with his new place in life working at the hotel.