The image in my head is that it's like the two of you are dueling. And his tactic is to keep his distance from you, than suddenly dart in, show you how he feels, then move out again. He figures that by maintaining his distance for awhile after moving in, it serves the purpose of letting the feelings sink in, and also lets them dissipate somewhat so that the next time you interact genuinely, it will be like starting at square one again. In other words, he knows the relationship isn't allowed to progress, so if he was consistently warm and perfectly genuine about his feelings with you, he feels the relationship will start deepening again and he can't allow that. But diluting the relationship to a superficial one is more than he can bear.

I think it probably also has to do with your intertype relations. Being that you're both Fe egos, you are both drinking in each other's feelings when you interact. I think Fe is sort of like a sponge that soaks up all the emotions in its path. If you were a logical type though, I don't think he would feel the need to be all or nothing, because you would be sort of like the emotional regulator in the relationship, not as susceptible to internalising emotions that might just be the overflow of a full heart. Not that they're not real, but he probably finds it hard not to represent his true feelings towards you, and you're not helping him by not being stand-offish. (c: So he feels he has to do the pushing-away thing every once awhile to keep the relationship somewhat balanced. It's too hard for him to regulate his feelings fulltime, so he does it in bursts.

That's the way I see it anyway. I could be massively projecting though. (c: