
Well, the way he approached him was pretty skivvy from jump. Like that DM asking if he masturbates and how he does it and then immediately tugging him into scenes without talking out details. Also, the contract he gave him to sign was fine for a draft but they should have talked more and garnered some trust between them before anything was signed. Stuff like that can be emotionally and physically draining on pets/subs. He doesn't really ask the submissive many questions and kind of make comments that a borderline if not completely manipulative so that the sub yields or feels bad if he says otherwise? Also, there was no safe word/action put into place for the sub to express when he's uncomfortable, only that he's never allowed to say no to his master? Then the one time it slipped out in an unrelated way he decides to leave and 'void' their contract right there in the middle of it instead of talking it out. He shows some concern in places but I'm not a fan.
Granted, I'm answering your question and diving into detail because you asked. I don't really have hella high expectations of many yaoi/smut series like this from jump. It's fine for art and naughty stuff but I'd never in a million years want him as a dom. phew. That's it! ╮( ̄▽ ̄)╭

I agree that the story isn't well thought out, but I do disagree that the only issue is the safe word. The uke is obviously extremely insecure, naive, and not quick to speak up for himself which the seme noticed and took advantage of. He liked that he was a virgin and commented on it, and quite frankly he's conceited with no reason for being so. Kind of grooming him there. Also, he doesn't explain any of the toys he's using, just dives right in.
Definitely, rules can be put into place in a BDSM relationship where the master can choose to not include their private life, however that doesn't entail being cold. There should be aftercare when scenes are finished, for one. A dom or master should recognize and address their sub/pets needs to make sure they're happy and healthy in the relationship and he doesn't do that. The uke constantly had questions, concerns, and worries he was too scared to bring up..which shouldn't be the case. That being said, he needs to be more verbal or he'll keep getting taken advantage of. ┑( ̄Д  ̄)┍ They're both helpless honestly.

Nah, sex only or not, aftercare is literally just the bare minimum for a master. He doesn't know he deserves that so he doesn't ask for it. But, don't call yourself a master if you're not at least willing to do that for your pet. They are basically strangers, I agree. And the uke doesn't need to find someone to help him become mentally stable, he needs to do that on his own and possibly find someone who's willing to be patient and help him cultivate that.
I speak as an experienced dom/sub, so this is me trying to educate rather than lecture. I wouldn't want anyone getting something similar and thinking they hit the jackpot cause the guy is hot. Lol It doesn't matter, this is a manga and we all know they'll end up together happily ever after or whatever.
There are so many red flags and this depiction of BDSM ain't cute. D<