I always thought Yu was more Moon than Fool, at least anime Yu. Characters who are of the Moon Arcana have a common trend of putting their projection of their own fears and faults onto others. They often tend to have trouble accepting themselves for who they are and, because of that fear, try to correspond to an ideal person. And like the Arcana, there is a hidden depth as to why they act in their behaviors. (Wiki)
If that doesn’t sound like Anime Yu, then let me talk about this.
Yu’s fears being alone. Naturally, you’d hang out with others to calm this fear, but fears don’t go away that fast. I mean, you saw what happened to him in episode 13 and 25. Yu also fears rejection and losing his friends and acts dramatically or very stubley upon receiving it, (mostly looking at you, esidope 25) and at the very least, freaks out inside, and tries to save it, even if it looks somewhat ciggly. He was willing to go though the relationship with Ai that in no why was healthy. Yu’s friends even worried about his well being, as he had no time for the rest of them, and he was constantly called by Ai. Hell, Chie even claimed Ai treated Yu horribly, and he doesn’t deserve such treatment.
For the trouble accepting themselves part of the Moon, Yu doesn’t have this as bad as the others, but it’s still pretty bad if your Persona goes back to a Shadow.
Corresponding to an ideal person, do I even need to say this? That the whole reason Yu will not say no. He has problems with understanding when to stop making people happy at the sake of his own toll. He tries to be this great person because he’s so deeply scared of being alone, he probably feels that if he doesn’t, people have no reason to accept him, and when that happens, Yu withdraws into himself and loses the confidence he normally portrays.
The hidden depth, is likely a lot of things, like the fact he probably had no real friends before Inaba, or moves around a lot, but I think it’s the fact that Yu views himself as a weak person and gets his strength from his bonds and being accepted by others. Without that, Yu feels worthless (at least, it seems like it) and thus, always needs to be around someone to feel like he’s worth something.
TDLR: Yu is more of the Moon Arcana then he is of the Fool.