Let's past forward... .. readers thought Keith cheat on him but it's not. And some hate him much But he's not a bad seme here.
I don't want to spoil you more but I'll let you know Keith Like him the first time they meet, though Keith doesn't know it was him. Eversince they had sex Keith's diccu won't get hard for others(woman). And what I like the most here seme's first sex with men was him. First sex and first in serious relationship. wooooo......
I think he is always in denial of his feelings due to his family affairs. Both his parent are men, I guess that's one reason he kept on seeing he doesn't like men, because he's parents relationship can't be call as a normal lovers or couple thing.
This is spoilers...
Basically they find out the uke is pregnant.. so there is a lot of back and forth of uke running away and the seme trying to catch him.. I don’t remember much but I think the main reason uke didn’t want to marry seme was cuz he caught him cheating *AGAIN* with someone in his room and so he ran away.. One of the security guard helps the uke and than the seme raids the place uke was sting in but the uke hides and they don’t find him.. than later on uke finds out his pictures are all over the news for being wanted or something and that’s when he finds that red haired guy with the cat who helps him.. but the seme eventually finds the uke and the red haired guy tries to stop them but the uke worries he( red haired) will get hurt so the uke says he will leave with the seme.. I think that’s how far I got..
For the cheating part to me it just felt like cuz he can..like it seems to me like the seme doesn’t like the uke as in like emotionally..he kinda likes having sex with him in the heat of the moment and I think he suggested marriage cuz he feels like he has to take responsibility for it.. but other than than he only shows care for the seme in like moments of heat..
And I am not sure if this was before or after the uke goes with the seme but after that they had sex again but after than the uke drugs the seme and says I think something like U are not gonna see the baby and I will never marry u or something of that sort.. but I could just be mixing up the timeline lol

woooo
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I'm excited much.....I already know what will happened next but still I really need to read the manhwa.