Cheating?

I’ve been my bf over a year. Recently he has trouble getting hard or staying hard. ( we’re both 18) like one minute he’ll be hard and then he’ll get soft from switching positions or putting the condom on. He was NEVER like this before. He jerks off the same amount since the beginning of our relationship and it was fine then. Idk what’s going on. Ik he takes a while to regain in his dick after cumming so a part of me thinks maybe he’s getting it somewhere else. Is this a sign????