Is because we don't actually know anything about him. Same with protagonists he doesn't know him yet seme has a lot of power over him.
I mean I don't hate him but I am suspicious of him he may be a really good hearted person but could also not.
the seme seems kind of fishy to me by his reactions and such
for example every time the seme wants to change the conversation which is making him awkward or similar he touches the uke to show affection and like that change the conversation, seems like manipulation to me, but its still to early to confirm anything
The seme seems like a nice ordinary guy who tries to make uke happy but it seems he has no clue what's going on or what should he do! But of course he helped the uke feeling better. .. idk why ppl hate on him while he's doing HIS best!
And uke is a lonely guy suffering from some sorta trauma that's why he's thinking so negatively ( which breaks my heart for him)