By definition, poly is about having multiple relationships. Polyamory-multiple loves.
It sounds like what you are wanting is more of an "open relationship" where he can have sex with others but not have love and relationships with others.
Maybe read the book Opening Up by Tristan Taormino. (Spelling of last name may be off). It covers a variety of open relationship styles including but not limited to polyamory. It also details some important topics to consider and discuss.
"Love As Thou Wilt"