Oz/Gil/Alice is pretty much canon! They just signify very different things to Oz. Gil is Oz's link to the past and the person he can rely on the most to him stable because more than anything, he needs that foundation, someone who can tell him everything will be all right, because while Oz doesn't really show it, he's incredibly cynical and bitter with himself. When he's involved, nothing goes right and he's very well aware of that fact.

Alice is Oz's link to the future. She makes him think differently, makes him feel differently about himself. The problem with Gil and Oz is that they lock themselves in their codependancy and don't seek anything beyond that. But Alice does, she wants to change and Oz finds himself believing in that change and vision she presents to him. Alice is strong and bright and Oz wants to follow that light that she has.

Often, I think Gil and Oz will most definitely lead to tragedy because of their own fixation of the past. But I secretly hope Mochizuki gives them all their happy ending.