OP, I feel for you. You obviously have considered “his point of view” hence asking the question. I don’t have to be a mum to see that YANBU in any way shape or form.
Some of us mean well in trying to support a new-mum relative or friend, but get a bit blinkered by what we want out of the interaction, and as a proud and loving Uncle Gantry, I’ve learned from my sisters and friends along that way. But there’s accidentally treading on toes and then there’s knowingly going against someone’s wishes and needs when they are at a vulnerable and exhausting time:
A well meaning person might, from the best of intentions, wonder whether it would be helpful to give an exhausted new mum a break by “getting away” from parenting her baby for a short break. Sometimes that can help, IF it’s what SHE WANTS. If this sort of idea comes to mind, the thing to do would be to ask the new mum. Don’t assume, ask. If she declines that form of assistance, her response is to be respected. In this case the answer is an unequivocal No thanks.
She is entirely within her rights to decline such an offer. Meaning that if she doesn’t want to, that’s a reasoned and reasonable response. Meaning, also, that she can say “no thanks” without feeling indebted or beholden for your intentions. The logical and loving next step would be to offer something else, and by all means with their input on what would help or be fun for new mum. It doesn’t have to be a complete surprise or a one off grand gesture.
If you, knowing she doesn’t want it, make elaborate arrangements for 2 things that she doesn’t want to happen, both of which are quite big deals, then any “bother” or trouble that you take is entirely on you. She doesn’t have to feel extra grateful for you in how much time effort or expense you took in arranging to override her preferences.
She absolutely does not have to resign herself to drawing on her almost-empty battery, to show “appreciation” by going against her own wishes and needs, and this would even apply if you’d cooked a meal made of ingredients she doesn’t like. Let alone getting out of her comfort zone (ā 30 min drive away from the baby she did not want to leave), then actively into a discomfort zone (clothing that is not made for comfort, even in the correct size), and expecting her to go along with it out of gratitude.
The meaning well, the thoughtfulness, the going to “all the bother” - none of this counts for anything any more if the man has a tantrum that she doesn’t just go along with it out of “appreciation”.
But on the subject of good intentions, then it bears repeating as many of the MNs have on here, so eloquently, that this mum needs to be listened to and supported. The issue here is that both of the forms of “support” thrust upon @BeccaBoo9 were (at best) misguided, because not only did they go against what she said, but both of them involved getting something from her. MIL wanted @BeccaBoo9 to give away a share of her limited and precious bonding time with baby. DH wanted @BeccaBoo9 to expend her limited energies and attentions on pleasing him. For a tired and overstimulated new mum, these are big asks. Here it was one big ask and then another. If she isn’t up for that, it’s not for either of them, or anyone else, to tell her that she should want to be.
MIL, dear lady, if your offer of help is contingent on you getting exclusive time with that baby, then it comes with strings attached. DH, mate, seriously. If organising a night away was a means of hurrying along access to the sex that she’s told you she’s not ready for, then it comes with strings attached.
Neither of these was a purely selfless offer for which she should feel grateful or beholden or feel obliged to have semi-consensual sex in uncomfortable clothes. As a man I would be horrified. Horrified. If I thought a woman was reluctantly summoning her last bit of goodwill to have sex with me.
She is totally within her rights to decline.
She was gracious and brave in going for the meal; she stood her ground and wisely said she would see how she felt. That’s more than enough appreciation; more than enough seeing of his point of view.
So, OP, as many of the more experienced commenters have said here - and I could not agree more - the fact that his reaction to learning that his Grand Gesture wasn’t the kind of support you need, was to disappear down the pub, tells you all you need to know. He removed himself from you and from any household chores and all of the nappy and caring tasks that needed to be done during that time.
I think the great MNs on here are bang on when they say, write your POV down, give it to him, and refer him to that.
(This was a long response; I follow MN AIBU content mostly for something non parental but I have learned so much here on what to do (and not) when being part of someone’s village, and this situation resonated with how I’ve seen “help” offered in the past.)