Yeah, pertaining to the negative side of 2s in relationships, (spoiler alert) Cas is going to get jealous when he starts to notice that Miles has a thing for Iris too cx He already showed a little jealousy when he first learned about Ethan (and before he knew Maisie was a girl) but Miles is a genuinely good dude, so he would worry that Iris would become interested in him since Miles is also more readily available at the moment. He's more codependent than he realizes, which is something he'll have to work on later.

2s are really interesting in romantic relationships. They're either really great together or really self-destructive. Sometimes they flip flop between the two, but there's rarely an in-between because they're so emotionally volatile.