I don’t think it would be a conscious decision: “Let’s see, I have this problem, so therefore I’m going to break up with my SO.”
But he may falsely ascribe his sexual problems to his SO, for one thing. He may not understand that she may be the person most responsible for keeping him alive. He may also be frustrated at the problems and wear that frustration on his sleeve in a way that makes him impossible to live with.
People do all sorts of things for all sorts of reasons, which aren’t always obvious even to them, much less to the outside observer. (In fact, sometimes it is only obvious to outside observers. Other times, what is “clearly obvious” to outside observers is dead wrong.)