As everyone else has said... it's time for The Talk! The poly talk, that is.
It sounds like he's not completely against the idea of you being with other people, but yes, the fuzzy guidelines (which you have probably bent to your favour, because you can) have probably dented his trust.
First off, though: what do you want?
Is being poly a need for you? If he wanted monogamy, would that be the end of your relationship? You have to be clear with him, and yourself, on your own realistic needs.
Cheating is cheating, poly is poly, grey area is whatever you decide it is. Hiding things is not great. Really not great.
Ok, so let's say he remains vague about what guidelines you two should have. Then you'd have to tell him that with no clear guidelines, you're going to end up doing what you want, essentially.
Can you be satisfied with your partner and "don't ask don't tell" hookups? It doesn't sound like it. It sounds like you need more, from my perspective. And that's ok if you do.
So you have to communicate with your boyfriend. Or your boyfriend has to accept that if you don't communicate, neither of you will be totally clear and problems will arise here and there.