My stepson hates me for no reason

My (45M) stepson (14M) openly admits that he hates me but doesn't know why. His mom and I have been together for 8 yrs, and there's been little change over that time.

I do my best to treat him fairly and go out of my way to do nice things for him. I have no interest in trying to be a dad of sorts, but try to be a solid influence and reliable resource. His dad lives close by but rarely has anything to do with him. He's with us 98% of the time.

I know it's not unusual for stepkids to treat their stepparents poorly due to the very real disruption of their lives and the pain that goes with that. However, I didn't really expect the open aggression to go on this long, especially considering my ongoing efforts to support him. And sure, he's an angsty teen, but this, to me, seems a lot more intense and consistent.

I don't really want to give up on him, but I'm also losing the will to do nice things for him when I'm feeling used. Whereas I don't try to be his dad, I DO hold him accountable to the house rules. I also do things for him as I would my own son (gifts, favorite foods, trips, etc.).

My wife tells me it's fine to stop going out of my way to be kind to him when he's consistently a jerk to me, but I hate the idea of treating the kids differently. His real dad isn't going to make up the difference.

We've gotten into huge arguments before, after which he tells me he was to blame and that he doesn't know why he treats me this way. Then he goes right back to being a jerk.

Any thoughts on building a better relationship?