I know one. He's just super introverted and needs a lot of time alone, and usually gets embarrassed after he's said something slightly squishy, so it's easy to see him giving some kind of huge awkward-but-heartfelt confession then going completely MIA for a few days.Why do they disappear, when they say they like you?
Your first problem is that he's an INTJ. I get the impression that they don't need anyone. In that case, no one needs them. Plenty more characters that are much more fun.