I've asked specifically about how strong emotions are received in a relationship. The three INTPs I've known (BF, guy friend, girl buddy <--- all super sarcastic) all say that they are very fond of strong, positive emotions. And that they really want to see it from their partners in a relationship. And when they have that, they've been the most open and true-hearted people about their softer feelings. I like seeing an INTP in that mode. <3
And INTPs can be very able flirts, even for sport. Perhaps a shy INTP might find it hard but being INTP doesn't preclude sport flirting. Esp on the internet. And esp if it's reciprocated. I think it's obvious when an INTP crosses over to serious pursuit though. They can be very direct. I suspect they need to feel strongly about the person, that there is relationship potential and that the interest is mutual.