The biggest piece of advice that I can give to new mothers when they aren't sleeping or have to hold their babies all day or have to breast feed at the dinner table... is to try and remember that it's just a phase. It won't last.
The thing that I don't like to tell them and the thing that makes me want to punch myself late at night, is that unfortunately, the good things are also a phase. "Oh, my angel baby slept for six hours in a row the last two nights! That's great! I think I'll have three cocktails tonight!" And then your darling baby decides to yank that carrot back and leave you starving for delicious carrots and also, hungover.
It has to be the hardest part of being a new mom. The ol' bait and switch. The sneaky bastards (that is, if your partner can't see the point of committing to the mother of his children in front of friends, family and God. Because, yeah, marriage is sooo stupid and the millions upon millions of couples that have gone before you are CRAZY. Or, whatever) wait until you're about to crack, turn up the charm, make you get that fuzzy feeling for them that you had in the hospital before the drugs wore off, and then they punch you in the face. Metaphorically speaking. What I'm getting at is that I strongly suggest you consider adoption. Like, in Anne of Green Gables: adopt a tween. The sleep training is over, you can put them to work on your family farm or at least make them mow the lawn and worse case scenario; they're out in a handful of years. Or you can always send them back where they came from with a nice note attached.