Do you guys dislike jeha bcs his past lover or about the marriage?

No it's not because of that
Jeha knows mong is going through so much right now and treating him like shit
And in last chapter he also told mong that he stop caring about her sister cause she is not blood related

I forgot about his past lover, who is that??

It's unrequited love who is dead now
So you can't say it's lover