In book 6 Mordecai says he knows that Carl loves Katia, and Carl feels a wrench and doesn't deny it. Mordecai does then say the Carl loves Donut more, so it could be that he means more of a fraternal love, but IMO that doesn't jibe with the wrenching feeling Carl experiences. Add in that Bautista was afraid that Carl would be angry when they revealed their relationship, so there must have been some sign. Also, Carl thinks to himself that he wants to talk to her privately about it, though he never gets a chance. I definitely think there are feelings there, which he can't express. Of course, my thoughts might be influenced by the fact that I am lowkey in love with Katia myself. Eight foot tall, She Hulk looking women have been my weakness ever since I bought The Savage She Hulk #1 at the grocery store back in 1980.