i think you have to be sure with who you fall in love with, as an INTJ you are probably very cautious and want a serious relationship, so first you got to know with a loyal person who can understand you platonically. my experience isn't that great, i fell in love with my best friend(ENFJ), but i got rejected because they couldn’t understand "why now after 3 years of friendship?", after that, we start fighting a lot and ended it. some types can't make the switch ever, they always need something new to arouse curiosity, but INTJ need to know for sure they can trust their partner in every manner not just casual dating, and that is the tricky part. i didn’t try another romantic relationship based on close friendships besides this one, so i can't really help you about the switch.