A while back I had this language-difference (not to say "argument") with a lover. I said that I felt grateful for the chance to meet and be close to her. She asked: given that I'm an atheist — grateful to whom? My thought was that gratefulness didn't really have to be attached to a particular giver; I could be grateful for something rather than grateful to someone. But it might be that "appreciation" or simply "gladness" would be more unambiguous descriptions.