It's a formula for more misery than you would believe. Learning about the mate is what engagements are for, and you shouldn't ignore what you find out. Constant argument is a terrible, terrible sign. It predicts nothing good. Please put this relationship out of its misery and find someone you feel cheerful and funny and free with.
Life is short.
Don't enlist in the Thirty Years' War. The sight of her shivering at the bus stop every morning is upsetting. Her family situation is kind of shaky, and her mother and stepfather are not very involved in their children's lives. And maybe she likes her ratty old coat. Perplexed in Pittsburgh Dear Perplexed, I vote for getting the kid a coat.