My boyfriend gets soft really fast

My boyfriend and I are both pretty young. We're both 15 and we were each other's first. I've noticed that he gets soft reallyyyyyy fast. Like he was getting a condom and it took like 30 sec and he got soft so I had to suck his dick until he got hard again. It was just really frustrating to me because if we stopped doing anything for like 10 seconds he would get soft and it was really frustrating to me because I kept having to suck his dick and I hate sucking dick but I never complain. Is it something I'm doing wrong that he would get soft? I just don't know what to do...