What you allude to in your first statement is incorrect for most cases, IMO. Staying together doesn't necessarily mean letting it decrease your happiness. It might just mean you have to get your happiness from a different place.
Often in life you're not presented with win-lose situations. Instead, you're presented with lose-lose situations, and it's your job to choose the least worst solution for everyone involved.
Often in life you're not presented with win-lose situations. Instead, you're presented with lose-lose situations, and it's your job to choose the least worst solution for everyone involved.