I'm not sure how you expect your husband to show you a "united front"? Your adult son prefers his dad. That's fine, that's normal and nothing your husband can say can change that.
He also should have put his son first when he was a child. That's also a normal, parental thing to do. Didn't you?
You talk about the fact that your sacrifice was far more than your husband's, that's weird!! I assume you mean you perhaps got stretch marks etc when you talk about appearance? Or some damage due to the birth? Sadly, that's a fact of motherhood and something your husband has no control over. Neither does your son. You chose to have him, he does not have to be grateful to you or feel guilty for any health or appearance issues you may have suffered in his birth. I don't care about my abundant stretch marks, they mean I was lucky enough to have my wonderful daughter. Who by the way much prefers her father over me, even though I was the one who looked after her on a day to day basis as I was a SAHM. She's a teenager now but still can be having the best day with me, but when dad walks in, she is straight to him. I love it, nay, I ADORE the bond they have, it literally brings happy tears to my eyes when I think how close they are, and I'm no sentimental fool. How could I possibly begrudge the fact that the two people I love most in my life love each other so much? And yes, my husband thinks it's hilarious our daughter prefers him more than me. But so do I!
You say he respects you, then that's all good. If he disrespected you, that would be an entirely different matter and in that case, your husband should stand up for you. But you can't tell an adult he has to prefer his mother because she made the bigger sacrifice for him. Or that at least he has to like them 50/50! 