An "I-Thou" relationship is an "I-You" relationship (casual relationship) on deeper, more authentic level (think it comes from an existentialist by the name of Buber). You can also have an "I-It" relationship with a person if you simply relate to them in an impersonal or instrumental way.

Didn't mean to imply that you were the type to 'come on strong!'

How do you know if he wants you to stay? A meaningful look. An electric silence. An erotic vibe. You know, the usual; only perhaps more subtle.