You should consider cheating, but make sure he is aware of why you would consider this. By discussing both of your feelings, you open the opportunity to a healthy compromise. Now this is not the only option; you could pretend that your Manstress is your boyfriend and make sure your boyfriend is aware that this is going on. So while you pretend that the manstress is your boyfriend, you pretend your boyfriend is your manstress during sexual engagement. Just make sure you iron out the terms of commitment beforehand and understand any risks involved, lest someone takes things too far.