Did he just turned on from seeing his ex love burning himself omg YOU NEED THERAPY

Wondering that too, I wanna give him the benefit of the doubt tho

Alone the lines of "got turned on that his lover was willing to do that coz of him but then got scared when it actually happened"

Exactly what seme was saying. He was happy because he realised he had such an effect on somebody. He knows he's sick.

I think he was horrified that he actually burned himself, but when he first saw it the sadistic part of him got excited, and that scared him and made him feel guilty, which then made him punish himself by keeping people away at arm's length since he believes he's dangerous.

I don't think his thoughts were that bizarre. It's a bit like how sometimes when you get catcalled in the evening, you mainly feel angry, annoyed and scared; but there's a small part of you that is flattered. That part might be a lot smaller than the rest, to the point where it's not noticeable most of the time, but you could also say it's twisted. I think we all have thoughts like that, that come from insecurities or hidden desires. The problem comes when you act on them (like the ex that set himself on fire to get the seme's attention and make him regret thinking of getting engaged like his parents want him to). Thinking "ah i wish i could hurt myself to get back at x person for hurting me" is very unhealthy already but actually planning and doing it is very malicious impulsive and manipulative. I guess that's the difference?