Boyfriend can't cum

My boyfriend and I had sex for the first time with each other. We've had sex only twice but neither of the two times did he finish. He stays hard the entire time and we are eventually forced to stop due to being interrupted by someone but that's usually twenty minutes in. When he masturbates he says his maximum is twenty minutes but it is usually more around seven. He didn't masturbate for a week to see if that was the problem. I realize that this app is for women's health but I was hoping someone had an answer?