What a tough one!

But of course your cousin has no idea of what they are asking you to do - they don't have kids!! It's unreasonable to expect them to get it - some things just don't make sense until you have kids yourself, this is normal and part of the change that happens to us all as first time parents. I think his response was perfectly fine.

I think if we all remember back to our Weddings we put a lot of planning into the day and lets be honest I don't think I have ever met one bride/groom who has had successfully met every guests needs, compromises need to me made and someone is always going to be inconvenienced.

We didn't wan't kids at our Wedding, our venue was small and we squeezed in as many guests as we could but invited our nieces (7 and 9) and cousins child (2) only because the rest of their/our family were there (who would have been the likely babysitters). It worked out fine. However NOW as a mother I would be much more accomodating to others with children as now I DO know the needs of a Mother and Baby. I honestly did not before.

We left my DS with Nan for the night for a Wedding when he was 4 months. He was BF so I expressed a lot before and between ceremony and reception for relief and rang/sms's my Mum at regular intervals. Leading up to the night I regularly had her settle him for bed etc (while I was there) so both her, I and he were all comfortable. While it wasn't ideal and I missed him like crazy on the night, it worked well. However with my Mum I can be completely honest with her and know she will follow my instructions to a tee, not sure if you have that relationship with your MIL.

If you are not going, then you have made the totally right decision not to go, the right age to leave a bub is when that Mum and Baby are ready. While your cousin may not fully understand that now, they will once they have their own. Be comfortable in your decision as its yours to make, but don't let it ruin or compromise your relationship with your cousin as he is in a different stage of life. As Mum's we need to follow our instincts!

HTH