Part of why Jiang Cheng makes such an interesting asexual/aromantic character is that ace/aro people are too often shown to be almost detached from emotions and only into science and technology stuff. Like they're fleshy robots.
But you know Jiang Cheng isn't like that. Every pore oozes his want and need for people in his life, people who love him and choose him. He wants so badly to have emotional connections, even if he's not good at them (which is a separate thing to his ace aspect imo).
If Jiang Yanli had stayed in LP with her husband and filled it with babies Jiang Cheng would have been the happiest man.
If Wei Wuxian had stayed and Lan Wangji joined him, he would have been happy.
But he ends up with none of that. He wants love so badly but he can't get it because of circumstances, his choices (forced or otherwise), or the fact that people don't prioritise non-sexual, non-romantic love as much as their counterparts. -I was gonna say except JYL and WWX but then reconsidered.
It's the kind of life experience that many, many grey spectrum people have to one degree or another and I think, even if you think JC is to blame for his bad attitude driving people away as much as circumstances, it's too painfully easy to see a part of yourself in his loneliness.