MIL made me feel unwelcome.

Honestly - I’d have found that situation a bit odd. I’d expect either you to have taken the baby while your wife stayed - or for you to go back with her. So - to be fair to your MIL - maybe she was just a bit thrown in the moment rather than deliberately trying to make a point?

Your wife is pregnant, breastfeeding and probably exhausted. MIL was probably surprised you weren’t going home to help her out…

You wouldn't expect him to leave your sister's party and she doesn't even like him? And then to expect without asking that someone will drive him the hour home?

He can't breastfeed the child to sleep so it would be pointless

There's no way this is a woman, regardless of how he answers.

@KeenSnail I’m with you, your mil’s comment did suggest you weren’t welcome.

She could easily have said it’s fine as you are family or if she were that bothered she could have asked sil herself, there was no need for her comment with a “I don’t know”.

Exactly this. You were clearly a bit drunk and being belligerent, and have set back what were clearly very rocky relations a mile.

No more to say apart from this

Give the guy a break. Totally normal, one person wants to go home earlier and the other person stays. I wouldn't expect my husband to leave under those circumstances. I think MIL was being snippy and there was no need for it.

"I haven’t always got on with my SIL, however over time we have disagreed less and less and I was under the impression the past was water under the bridge"

This was clearly only YOUR impression.

What did you disagree about?

They don't want you there without your wife as a buffer, they don't like you, probably because of whatever went on with your SIL and the fact you thought it was fone yo leave your wife to drive home, pregnant, alone after a long day to sort out the toddler by herself.
I'd be raising my eyebrow at you as well.

Are you a woman BTW?

I can't imagine why you would want to stay at your wife's sister's party without your wife and child being there? You'd been there all day anyway - I find this really odd. Especially, as you have stated, you haven't always got on with SIL. Why would you let your pregnant wife and young son drive an hour home (to holiday home) on their own - just so you can stay and continue to drink at the party? Weird. If my daughter's husband had said he was staying in similar circumstances then I would have acted weird too and been unimpressed with my son in law's behaviour.

To be fair I would absolutely socialise with my in laws without DH (and I do, fairly often). In this scenario though he should have gone home with his pregnant wife to help put the toddler to bed.

It’s weird that she’s going home with dc and you’re staying on to socialise with her family alone.
It would be equally as odd if you’d both went to visit your family and she’d stayed behind while you went home with the kids.

I get along brilliantly with my in laws but still wouldn’t do this

It still looks shitty to stay without her when you are on a holiday. So MIL probably had a momentary blip surprised you weren’t going to help your wife (she’s carrying your child so obviously you need to do more at the minute) and answered that she didn’t no if you could stay. And in return you over reacted and were rude to her, you owe her an apology

You should at least have offered to take the baby home and leave your wife at the BBQ or even gone home with her. You two have a child together, you two are a family unit. Whatever the issue between SIL and you your MIL knows the details, hence her comment.

I haven’t always got on with my SIL, however over time we have disagreed less and less and I was under the impression the past was water under the bridge.

My guess is that all the disagreements you had with your SIL still rankle with her and your MIL. Your SIL sounds like a generous hostess who makes you welcome for your wife's sake ... but you were outstaying your welcome by asking to stay on alone. Then you were extremely petulant.

I wonder what all the past disagreements were about?

Even more so you should have gone with them, rather than leaving your pregnant wife to drive herself and a baby home, whilst you invited yourself to stay with her frankly celebrating. Unbelievable really. Your poor wife.

You make your wife a cup of tea. That's what you do for her. You're doing the other stuff because they're your job. Your children. It's not for her. Just the cup of tea. Just like her doing the evening routine isn't "for you". I bet the evening routine includes cooking for you too, which involves a bit more than a kettle.

My dh would do anything. Sometimes, even whilst pregnant he does the family thing and I happily fuck off home!! On other occasions he takes kids home and I stay.

My bil is no contact with his family. He’s treated the same as dsis. Either can go home or both.

No one is assuming anything. Even as a present, equal parent- it’s still very weird to let your pregnant wife go and deal with toddler in a different place- alone, so you can party with her family.

You should have been heading back and running a cool bath for her, then maybe enjoying some adult time yourselves.

No, that’s not what people are assuming. But in any event, it’s the optics - it was your wife’s family and you happily sent her back when pregnant to do bedtime on her own so you can stay out drinking with her family. Her mum rightly raised her eyebrow at that and you got offended.

Well done, you're doing bare minimum basics and didn't step up for a special occasion.

Yeah, they felt you were being a flakey dad and husband drinking while your pregnant wife goes home early to put the baby to bed. At an event with her family. I agree with them btw. The bar is low for men clearly that you're offended by this

This is EXACTLY what it was...
She was leaving her SISTERS wedding early and pregnant you wanted to stay and party instead of stepping up and giving her a night off or helping.