Today's order of business: Dean Winchester is aplatonic. Let me explain why.
To start: aplatonic people do not experience platonic attraction. They do not have any desire to befriend specific people. I am going to assume that you all are familiar with asexuality and aromanticism. It's the same exact thing but for friendship. They often don't want friends in general, although of course not necessarily. Some aplatonic people are indifferent and don't really care if they have friends or not, and some like having friends despite the lack of attaction. The key is that if you're aplatonic, you don't meet people, even really cool people, and go "hey, I want to become friends with them." Even if you have friends, they tend to be pretty easy to drop if life changes because you don't feel that inherent connection to them.
Dean? Throughout the show as I've seen thus far (seasons 1-4), he never exhibits any desire for friends. He doesn't want to keep any specific people around, and he doesn't want friends as an abstract concept, either. The whole thing never enters his mind.
This is especially noticeable because Sam is so clearly alloplatonic. He's always looking for connection with others. Every time he meets one of the special children, he wants to keep in contact. He gives out his phone number to Andy and actively searches for Ava. In early romantic/sexual encounters, like in Provenance (1x19) and Heart (2x17) he seems much more interested in befriending these women than sleeping with them. In After School Special (4x13), the death of someone he was friends with for a single month in high school absolutely guts him. In Dean's flashbacks to high school, he doesn't even try to make friends. He only cares about hooking up with girls.
The only real exceptions I can think of are his relationship with Cassie (1x13), which is still far more sexual/romantic than any kind of friendship, and Richie (3x04) who is a fellow hunter and thus more of a coworker than anything. Yes, you certainly can be friends with girlfriends and coworkers, but that usually isn't the defining feature of either relationship. Besides, if his feelings for either of them were especially strong, I think he would have kept in contact with them. He runs into Richie again by accident, and he never seeks out Cassie again after her single episode.
The contrast with Sam makes it pretty obvious that it isn't just that friends are impractical given Dean's lifestyle. The same goes for Sam, but he still obviously wishes he could have them. It also means that it isn't a matter of desire for friends getting in the way of the plot or the writer's vision for the show, because Sam displays platonic attraction all the time and the show still works.
Now, one could argue that he does want friends and simply represses that. It is true that Dean represses almost everything. However, Dean is not actually good at repressing things. There are always cracks in the facade, and these cracks are displayed very clearly to the audience. He thinks he puts up a decent front, but time and time again, characters (especially Sam) see right through him. But when it comes to loneliness? Desire for connection and relationships outside of his family and sex? We don't see a thing. Dean is only lonely when separated from his family. He very much does not need anyone else.
If Dean wanted friends at some point but learned to repress that or ignore that desire? We would see that. We are shown countless times all the dreams and desires he needs to set aside in service of hunting and family, and friendship is never one of them. Even in his dream reality in 2x20, he doesn't have any friends at all.
Now, I am aware that in later seasons, Dean makes friends. That said, from experience in the apl community, it is pretty common for us to end up with friends whether we want them or not. Alloplatonics enjoy adopting friendless people. Sometimes people just keep showing up in your life and you're like "well... I guess we're friends now." Not feeling platonic attraction doesn't stop us from liking people or getting along with them once the relationship exists, we just don't have that feeling of attraction compelling us to start a relationship. I personally have loads of friends, and they're mostly by accident. You have enough good conversations with a mutual or someone in a discord server or someone irl and they tend to stick around. So while I know Dean makes friends later, unless he actively seeks them out and initiates the friendship, that really doesn't have any bearing on if he's aplatonic. Besides, the fact that in 4 entire seasons he doesn't do that at all when Sam does multiple times is more than enough for me.
To put it very simply, why do I think Dean is aplatonic? Because Sam is lonely in general, but Dean is only lonely when separated from Sam and/or John. Family are the only people he wants or needs.
(A disclaimer that aplatonic people can absolutely want romantic relationships. Dean just never demonstrate that. They also don't necessarily have any attraction to family either. That's called being afamilial. Dean just very obviously is not afamilial)
Edit: I've finished season 5 and yeah, this still completely holds up.
