Actually, I think a better title for this is "Why didn't you not marry X, given that you're so unhappy with X now?"
I married my H because I was young, idealistic, and stupid. Being idealistic and not a fortune-teller, I didn't know that the following things would happen after we got married. If these things had happened before we got married, I hope I would have been brave enough to not follow through with getting married.
H cheated on our taxes one year.
H was let go from his job but didn't tell me, even when I consulted him about my plan to quit my job to be at home more with our young children.
H was unemployed for more than five years. When I could no longer bite my tongue and said anything to him about looking for work, he told me that my asking him was keeping him from applying for jobs.
H was fired again six years ago. He has not applied for any jobs.
H again suggested we cheat on our taxes.
When our children became preteens, H started withdrawing from them and me. Apparently, children are only worth taking care of when they're little and you can play with them.
there's more, but I think that's enough for now.