I know this is personal, BUT....?

I have to get it out there. Why would a boyfriend whom you've "been with" thousands of times (ha, a little exaggeration here, but to get the point across) without any "protection" ever, suddenly refuse to do anything without putting one on? We both have been tested and know we're clean, and he said that wasn't the issue, but wouldn't tell me exactly why. It just really bothered me. Not that you really need to know, lol, but then he took it off halfway through anyways. HELP!