A few more thoughts...
"How do you think I felt when my daughter took me to a baby shop when I visited at Christmas and we saw a lovely pushchair but on telling her husband later the first words out of his mouth were...it’s not going to be too heavy for my mum is it?"
IMO, it was insensitive to say this in front of you, even if he knew his mum, the PGM (paternal grandmother) was going to be doing some childcare. I get that it hurts b/c it's one more reminder that PGM is going to be w/ GC more than you. I could see having a good (quiet, unbeknownst to DD or SIL) cry over it. But then I would let it go b/c it's just a practical matter. I'm sure SIL wasn't thinking of how his comment might affect you and didn't mean to be hurtful.
"Basically you are all saying suck it up. That’s fine but it loses me my daughter and grandchild. I thought I was close to my daughter but maybe I am wrong. This is hurting me so much."
And my heart goes out to you. I don't think you're losing DD and GC , though, just that the relationship w/ DD is changing and the one w/ GC will be different than you hoped. So yes, you can throw up your hands and walk away - or you can make your interactions memorable (especially as baby gets older) and special for the both of you. I hope you choose the latter!
Angela Rayner lashes out and calls Sunak “pint sized loser”.
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