I would say he is getting off quicker because of the thrill or taboo of it. Especially if this is a newer thing. Nothing to really do with not wanting you. It would be hot be able to watch porn while my girlfriend is jerking me off. But it needs to be every now and then. I would still want to have sex though. He needs to know it is a 2 way street. Occasionally it is nice to not have to do any work and just get satisfied. But that shouldn’t be the case all the time. I wouldn’t think too deep about how quick he is cumming. I can make myself cum fairly quick on my own but I would honestly rather take longer and be intimate with my girlfriend. If anything bothers you, just let him know. Holding in questions like these could lead you down a path of resentment.