I think that the apocalypse brought Warren and Max closer. Like, not to say there was ever a sort of rift, but to a degree—I don't know, I don't feel like Max was full-heartedly involved in their friendship prior to this. This is just a feeling, not a fact. And the concept of him liking her? Ew. She takes a blind eye in episode 1, but she seems to easily talk about this with Kate in episode 4. (Only saw the gifs, not the game play) I find it incredibly ambitious as to whether she has any slight feelings for him or not with the passing of episodes. But, to see him with another she gave a certain type of slow staring reaction. And she optionally calls him cute in a oh-so science-y way on his whiteboard. Anyway bottom line without any deep talk of relation progress, my interpretation is that with him being the only other person knowing she can rewind time, and as he helps her one way or the other in every episode: Max has grown to treasure him more and more.