Is taking a break from each other completely out of the question?
That means, I dunno, 3 months apart, not dating each other. You're both free to date other people, with the implication being that you can sleep with others but of course take all proper precautions, get tested, etc. afterwards.
If that is the situation, then he might not do anything at all. After all, sexual partners do not necessarily pop up out of nowhere. Plus he may be interested in being the only one who can step out, whereas if there's a possibility that you can do the same, he may think twice. But do recognize that this may kill off your relationship.
I had a BF who wanted us to have a more "open" relationship and become less exclusive, after about a year or so of dating. It was all dandy until I told him, "I'm going to avail myself of the option." Because, you see, P__ thought it was a fab idea for him
to be able to date others, but not for me
to. We broke up over that.