Galvin had never expected to come back, not even for Luke - especially not for Luke. The whole point of him staying away was so Luke could have something vaguely resembling a normal life, undisturbed by freaks and half lives.
But Luke was a Van Helsing, so Galvin shouldn't be surprised it didn't work - they attracted trouble like moths to a fly.
So the staying away approach obviously wasn't working and he was going to have to show Luke how to protect himself, the one thing he hoped he would never have to do for his godson.
But what he happened had happened, and there was nothing he could do about it, so he should stop complaining.
With Mina on his side he hoped that he could protect Luke from the worst of it - after all Mina could see what was coming, and that had to help.
But no, Luke was more like his father than he thought and it shattered Galvin's splintered heart into smaller pieces when he saw it. There was something about the way he moved, the way he talked - what he said - that made Galvin flashback to when he was Luke's age, he and a different Van Helsing thinking they could take on the world and make it out unscathed.
They had been so wrong, and so foolish, and it had taken them to lose too much for them to realise it.
He wouldn't let Luke make the same mistakes - the boy needed to toughen up a bit, become more realistic about the world. Not everything ended well, no matter how much you hoped it would, and Galvin would teach Luke that if he had to.
Better that way than to have a freak do it, probably with the death of Ruby or Jenny.
So Galvin did his best, to protect his godson and to open his eyes, so that when the freaks came Luke could hold his own.
If Galvin gets hurt, well that's accomplishing both his aims in one (because nothing opens someone's eyes worse than someone getting hospitalized, he knows that better than most).
And Luke brings him grapes, so he must be doing something right.
(He doesn't really know, this is the first time he's tried the godfather thing in years - he's kind of forgotten.)