He said Mi Eun will regret it if he finds out, this is getting curious and suspicious

I think it's because Mieum thinks so highly of his father and Jitae doesn't want to ruin that
Idk I might be wrong

Yepp, this. He mentioned before that he can't even believe his father would borrow money (that is what Jian told him that his father has a huge debt, tho it is probably a lie, but still his father is not a good person). And based on what his father did to Jitae he doesn't deserve to be saved

I hope he dies