Lots of people "go a little crazy" when they suspect their long-term partner is cheating on them.
I think Lauren kept it together waaaay too easily when the husband she professed to love died suddenly. It barely inconvenienced her!
I don't think anyone expected Brad to stay with Terese after he stopped loving her. It's the way it's been done - with Terese's natural feelings of betrayal being painted as unreasonable, and Brad and Lauren's almost complete lack of guilt at the hurt they've caused - that's the problem for me.