What is okay in an open relationship?

Me and my boyfriend are currently living in separate cities and so I pitched the idea of opening the relationship purely for sex and only while we’re apart for a long period of time. He seemed enthusiastic but now i wonder if he’s even considered sleeping with someone else, which makes me feel guilty (which is stupid because we agreed on our relationship being open). Now i obviously don’t want to abuse the fact that I’m technically allowed to sleep with others the same way I might if I was single, and I only want to talk to people if I start feeling extremely desperate, but also kind of want to be reassured that I can.