What do you mean, staying in a marriage is heartless?

Marriage is like a castle peak, you can't stay. Even if you keep it, it will become ruthless. The sentence "Keeping the castle peak in marriage is heartless" means that marriage can't keep the castle peak, and even if it can, it will become heartless. It expresses the possible problems and contradictions in marriage, as well as the emotional alienation and mutual harm between husband and wife.