Sure. The reason he can't cum is likely because his mind has been conditioned to think this is wrong.
The reason he came is the same reason alcohol gets so many people laid... they stop over thinking everything. I'll be he can come just fine on his own. Keep in mind, this has NOTHING to do with you. There is nothing wrong with you.
All he needs to do is relax and feel comfortable. If you can find out what is going on in his head, all the better. If he is worried about God, or pregnancy or something else and you can get him to talk about it, that would go a long way.
Alcohol might help again. Or you could try having him watch porn while you go down on him, headphones might help block out the world around him. His mind might relax as porn might be his normal routine. Then his mind might transition to the real world and he won't need his internal imagination to get off. All of this is just a thought, not everything will work for everyone.
He might also be gay. If he is, trust me it isn't because of you.
I'm suggesting unconventional steps because you have made a good effort with little results. Again, this isn't an issue with you.
It’s not you. Alcohol usually makes it take longer. Reasons why he has trouble coming:
1) he watches a shit ton of porn so he’s desensitized his brain to normal sex acts
2) he uses a death grip when he masturbates; again he has desensitized himself
3) he’s on meds of some sort, drinks a lot, or takes illegal drugs
4) stress
A very few guys just have a difficult time getting there. That’s unusual, though. Most men have the opposite problem.
* antidepressants are particularly known for this side effect
Scroll Down to Read Other Opinions
What's Your Opinion? Sign Up Now!he’s addicted to porn is the reason and it isn’t you
Ask him what he wants in bed and do that
Is he on SSRI anti-depressants like Paroxetine or Fluoxetine? ( SSRI means Synaptic Serotonine Intake Inhibitor ).
Don’t have sex while drunk. Let him wait a few days, tease him during those days.
I find that I cum quicker if I get oral.
We start out with me going down on her. Then fucking her till she cums. Then she blows me till I cum. I usually pretty quickly because I am extremely aroused by that point.
He is probably gay or at least bi.
Change the position until you find his weak point, everyone of us has a position we can't control ourselves to, and might cum quickly
For me my weakest position is the doggy style
I keep it to the end as it gets me cum soo fast after thrusting the ass
Are you sure he enjosy to sex with you?
Sexual Relationships 
Sexual Health 
Superb Opinion