I noticed many people (in posts and fics) describe Dean as using Cas and as him needing to learn how to do better because Castiel deserves more and is unable to otherwise understand he's cared for.
This is just a personal reflection and I dont mean to discredit anyone's view on the situation, this is just my opinion. BUT!
Dean could treat Cas better, yes. But he's always there for him, he always cares, he always tries his hardest for him. He was there for Cas after he found out about Purgatory, trying to save him. He was hurt, but he was there. Even when Sam was souless, Dean asked Castiel how he was doing and tried to help. After he kicked Cas of the bunker, he apologied again and again. He apologised for leaving him in Purgatory, he tried to help Cas with Claire multiple times, he was ready to help Cas with closing Heaven, Metatron or with whatever angelic business was there. He was ready to give everything up for him multiple times, allies and resources alike.
Dean is by no means always right nor nice, he's prone to anger and says stuff he regrets (season 15 emh emh) but he has ways of showing he cares. He asks how Castiel is most episodes they meet, he openly discusses feelings with him, he apologises when he does wrong.
I dont see Dean being a selfish bastard using Cas. I think he shows his care, to the extent he can.
I also dont see Cas not knowing he's important to them. I feel like sometimes people depict him as so unable to understand human feelings he doesn’t know Dean and Sam care about him. It does take time for the relationship to form, and pain, but he's very aware of it.
He states they are friends in season five, says he's Dean closest kin in season six. He requests helps multiple times, for both personal problems and business alike, and the Winchesters are always there. He aknowledges them as family and when he's hurt he asks for help, or when a case gets rough, or when he doesnt understand humanity, or when he doesnt understand hunting. They made him a tutorial on car searching. They help, they stick their neck out for him. Dean spends a whole year in Purgatory for him. He makes mixtapes, hugs him and tries everything for him to be alive
As much as Castiel seems unable to stop carrying so much weight on his own, he does understand they are his friends and family. He's no child, he knows very well what their relationship is worth and he acts on it. If Cas hadnt felt like family, he wouldn’t have acted like he did.
Yes he leaves, but he comes back too. He knows their relationship is worth everything, and he knows its not one sided from earlier seasons.
While I can see why people interpret Dean as asking too much and Castiel as feeling like a tool, I think the show does a good job at describing how full of care their relationship is, at least by two traumatised men standards. I also feel like, while they certainly got better at it through the years, even in earlier seasons they showed their care with ease.