i agree with soror about the hole oral sex part, you should try stroking it for him while your mouth is on there. if you grow tired from just bobbing your head anyway, that's what i do when my guy is taking to damn long and i want to hurry him up.
For the most part, what he's describing is normal. Erections do vary depending on the day, mood, point during sex, etc. It just happens like that - it's nothing that you did, so if you are (like I once did) wondering if it's your fault somehow, I assure you, it isn't.
Masturbation will not effect his performance, aside from potentially giving him more staying power during sex if he has masturbated/ejaculated recently.
Being unable to ejaculate from oral sex is tricky, because the truth is that he probably can, he's just nervous or anxious about it, or the timing is off. Remember that consistent, repetitive motion is what helps an orgasm with both males and females, so if you are unable to continue a consistent rhythm for long enough to bring him to orgasm (and no one will fault your for that, giving oral sex can be hard damned work), he might -think- he can't do it.
My advice is to give him oral sex anyway and eventually he'll be relaxed enough to orgasm/ejaculate. Don't talk to him about it, that will only make him more nervous, just gradually warm him up to it and make it more normal.
But - this is just my opinion.