That would be doing you a service, at their expense. They would have to endure discomfort in order to provide you with comfort. Why would they do that if they don't want to hang out or be friends with you? They have already determined that they cannot receive much/anything from you, so what do they gain from comforting you?
As for cheating, well, that's another concept. But, in that case, what would be the rational choice?
The cheating person can do one of two things: tell their partner that they're cheating, thereby ending the relationship--or at least losing one sexual--or otherwise--resource. Or, they can try to lie and try to maintain two sexual--or otherwise--resources.
Two is better than one.
