I think the thing with McCoy would be that they are sources of pain, but like everything, there are many different things that cause pain, and thus different outcomes to getting through that pain.
In TFF (which, to be honest, I'm only a fan of how Kelley played that scene, I thought the scenario itself was a little too convenient) it's implied that was perhaps something that drives him towards being a doctor. The divorce, on the other hand is something he can get over easier, but which drives him into a specific place where he can be a doctor.
If in the first film they were 'kids' (and at the end of the day they weren't really kids strictly, apart from Chekov, they were young adults although sometimes there can be little difference because life isn't always deadly serious at those ages yet) then I'd surmise that maybe the second film may present an opportunity for them to 'grow up' and become adults. They have the responsibilities now that they were just being presented with as they found their roles in the first film.
I mean, Kirk will always be horny..................but he might be more constructive in his sleeping arrangements next time!
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist