He climaxed - that should be all the evidence of pleasure a gal needs! Your boyfriend sounds like one of those men who become inexplicably mute when they're in the throes of passion. It can be quite disconcerting at first for a hardworking lover, but if this is your boyfriend's true natural style (rather than a sign of inhibition), then it's something you should try to accept - after all, I'm sure you don't want him to put on a sound show especially for you. But check in with him from time to time (not when he's climbing towards an orgasm but afterwards) - ask him if that was nice; if he'd like you to do it again like that next time; if he'd prefer it done slightly differently in future. I'm sure you'll be able to judge from his feedback if your technique was to his liking, even if you're simply weighing up the warmth in his grunts!
As for your handjobs: I doubt you're causing pain. Your boyfriend would find it exceedingly hard to hide his distress if you were genuinely rough-handling his most treasured asset. What you should know is that most men enjoy a surprisingly firm hold on their penises - if you've ever seen a fella masturbate, you'll know just how hard they yank on themselves in the run-up to orgasm. So unless you hear him squeal, I think it's safe to assume you're touching him in all the right ways.