In my opinion I don't think Tess should force her feelings into him, afterall she's been doing that since she was younger. He has alot of things that he's gone through and he's trying his best to live the new life that he got. Tess has had it well and she acts very spoiled at times which probably makes Art see her as more of a little sister. She should know as his "friend" he has alot to deal with and she hasn't really provided much help. It's the grandpa that been helping him more than anyone else to get used to the concept of mana and such. I think it's Art's own way of letting her down softly because no matter how much you love a person one sided unrequited love ain't going to get you any where.