Having Sex While Having Period

So lately my bf has been getting more aroused than usual and today he has asked me to do it while I’m on my period. He has previously denied wanting having sex while I was on my period because he thought it was nasty, which I was fine with it since I did told him I bleed a lot (medium to heavy flow) during my period. We been together for six years now and him finally saying that makes me excited but as soon as I told him it’s best to have a condom, he started questioning me why I wanted to use one when we don’t have problems when we been doing it for the past year now since I started using birth control. I need help to explain him better before he gets the wrong idea why I want to use a condom. I just want to be super safe doing that for the first time.