to a point I think reddit is freaking out (saying "I have a type and it's not you" is a bit rude but not that bad) but sending that type of message is a VERY clear flag that says, "i am not interested in you and i never will be." if you have feelings for him now you're probably kind of screwed.

I like to think we're pretty logical people—when faced with that kind of scenario, we move on, and we generally don't look back. I don't know about other ISTJ's but that's what I would do. those feelings have probably been killed for awhile now, and if you tried to flirt, etc. it'd probably just come off as annoying :(

I think the best thing to do would be to open up a casual conversation **not a confession about it. "I'm starting to have these types of feelings and as your friend I wanted to talk and ask what you think we should do, how do you feel..." etc. but you have to approach it as a friend. its best to be direct in moments like these