having a problem finishing up

For a few months now, when my boyfriend and I have sex he doesn't cum. He says it's not me. He has no problem getting it up or even having sex. He's been under a lot of stress with his classes, work and his parents have just bought a house that he's fixed up. He says he's very tired and doesn't know what's wrong. When he can't finish, he gets frustrated with himself. He also says he tries masturabting and has the same problem. Should we go get him check out or just wait till the stress goes away and keep trying. Please help!!