What Causes Purple Bruise On The Rim Of Penis?

My boyfriend and I were in his room yesterday and when I went to give him oral I noticed not only the purple like bruising but like a whitish color a little above the rim of the penis. It wasn't very high on the head maybe an inch or half inch. It wasn't quite even around it. I asked him about it and he said he didn't know and thought it was nothing. Now we have been apart for almost a month. Due to a break up. No he says he wasn't with anyone and all he has done is jerked off. So is this serious, can it be from him having oral or sex with someone else. Maybe using a condom or getting head from another woman?