Adding to what's been said, as long as you're picking the more affectionate dialogue options in general you'll be on the right track.
Him pulling away and being cold or difficult after being warm is normal. Well, maybe not "normal" exactly, but you're not doing anything wrong gameplay wise.
There are a couple of times I do think you need to hold back though. Like with the hug/kiss choice early on. I always go for the hug because it feels nicer and has the better dialogue afterwards. Trying to kiss there just sort of ends the scene and makes him freak out. I might be wrong of course, but the hug always plays into the "be patient but loving" path I always try to steer Dave down.