That is not the issues. This submissive doormat mc is not a new trop and it's something I kind of enjoy if done right. The problem is blatant disregard to the plot that the author themselves chose. Look at the synopsis/ summary. It's a revenge plot. Ml killed mc's mother, the one who raised him and the only person he is closest with for a HUGE chunk of his life. There has to be some consequence, a level of emotional depth that keeps whipping mc with emotional disgust, hopelessness and despair every now and then. Him falling in love is not an issue, the issue is it is done poorly. There is no high emotional tension. Fyi, Wei WuXian ain't letting it go if he was here. lol
It's expected this way since they titled this as toxin! I'm explaining to you what to expect this story since they titled this as toxin. And base on the plot scene if you don't noticed uke had a lot of misery and nightmares due to his guilt and btw, there is a plot holes of the event , they never showed who really command or killed his mother !

This bitch should have nightmares of his mother eating him alive everyday! How can one choose a killer of his mother as his lover, i could die to not be in a same room as him and bitch is straight up fucking him. Bro just think na? His mother raised him for years just to be with killer of his mom and abuser of himself!!! Whatever, happy be-lated mother's day