Fighting for a marriage

Why is it shameful to not fight for your marriage when you didn’t cause the issue that has occurred. Say a spouse cheated.. why is it “people are willing to throw away Marriage just so easily!”. In all reality cheating was a dealbreaker that was talked about before you two got married. Something you don’t tolerate, people will expect you to work through it and stay with that cheater. Then shame you when you don’t want to fight for it