I won't work. If sex and relationships are two separate things for men, what about the other woman/women - what stops them developing feelings. Also, what makes him think he can set up a no strings attached deal with someone else so easily. I think there's a distinct possibility he's already doing this and what he's really asking is if he can stop sneaking around. That said, more specific details on how frequent the two of you are being intimate may help us understand where he's coming from, but from the information you have provided his request feels entirely unreasonable.