When my husband quit, I felt so awful and helpless, because it was really something only he could do. I couldn't quit for him. But I really was very helpful, just by being his "rock". He never wanted to talk about it, but my job was to pretend to ignore it. Not say "wow it's been 5 days, great job!" or anything. If he slipped, he told me (he tried to hide it at first but that wasn't cool with me) and I wouldn't judge, I'd just hug him and say "no worries, you'll be all good tomorrow". Sometimes he'd say "wow I'm really having a craving" and that wasn't an invitation to discuss it, but it was a great cue that I should find some way to distract him.
And yeah, he got pretty irritable for a while, you just have to suck it up. And a pack-a-day long-term smoker has some nasty physical side effects of quitting, like horrible itching (as the body releases toxins through the skin) and nasty loud coughing up what looks like gooey black tar (which had been in his lungs for years). It's a good thing - the body getting rid of all the bad stuff it's been holding onto - but it's hard to go through.
My husband tried for years to quit, everything from cold turkey to ramping it down, the gum, the patch, the pills, you name it. What finally worked for him was a book called (I think) "Quitting: The Easy Way"; the author's name is Carr. It basically just says "you know smoking sucks, you want to quit, so just do it", which seems almost too obvious, but somehow it totally worked for him. He said "ok this is my last cigarette" and that was it. That was over a year ago and despite the occasional craving (I don't think that ever goes away) I really believe he's never going back. He likes being able to breathe :)
Grats to your boyfriend, and I hope both of you make it stick!