Absence make u want the person more?

Seems like the longer we dont see each other, the more my bf wants me (doesnt ignore me, gets sweeter, etc). But for me, I start losing interest if I don't see him after 2 days. Also, if i send him gushy txt messages, he kinda avoids me. But if i simply txt him back "k, cya" he wants me asap. Um....why?