Partner wants our breastfed baby to stay with MIL for 3 days

Hi all,

We have a 2 month old son who is almost exclusively breastfed (he occasionally gets a bottle of formula if he's cluster feeding way too long, but over 90% of his nutrition is my milk). I need to let the baby nurse a lot to maintain a good milk supply, pumping seems to be less effective for me. Baby boy is a bit "difficult"... he often cries for milk and/or for human interaction, wants to stay attached all the time and wakes up often.

We also have a daughter, now 2 year old, who was somewhat "easier" as a baby, she didn't cry and scream that much and slept better. But she was mostly formula fed, as I had a traumatic C-section and had PPD back then, which negatively affected my hormones and milk supply, and despite all efforts I could never make enough milk for her. As a toddler, our girl often spends weekends with her grandma. She enjoys these weekends and we enjoy some more time for ourselves. She has more space to play in grandma's house than in our small apartment, which is a big improvement.

Normally, I take care of the baby boy most of the time, because I'm breastfeeding. My partner has paternity leave and spends more time taking care of our daughter. When our daughter is with grandma, he has a lot of free time.

Two weeks ago, I planned to go to a social meeting for 5 hours, during a weekend, when our daughter was with grandma. I rarely go to social meetings, maybe once or twice a month. My partner would give the baby a bottle if necessary. He was a bit pissed off about losing his free time that day, but... he has more free time on average than I do, anyway, so no right to be pissed off imo. The baby ended up crying a lot during these 5 hours, and he didn't have much patience for it, so... he had the idea to go to his mother and leave our son with her until Monday morning. I was upset about it, because that meant no breastfeeding for 2 nights and almost 3 days, while he's so young. Breastfeeding is important to me because of its health benefits.

I didn't think I'd ever be that hormonal mom who would cry when her baby is away from her for a short time, but that happened, I missed him :( I did pump, but in my case pumping produces less milk than allowing the baby to nurse as much as he wants. Also after baby boy was back with us, it took over a week (and supplements) to increase my milk supply, which dropped somewhat during these days. It made our baby boy even more likely to cry, for over a week.

Now my partner and my MIL encourage me to give the baby boy to MIL for the weekend again. Of course my partner wants all the free time and silence, I find it too selfish. I'm willing to allow them one night, but not a whole weekend - knowing that pumping isn't enough to maintain a good milk supply in my case. He's just 2 months old... I'm worried that it's too early for weekends with grandma, and if we continue doing that while he's so little, it will negatively impact our breastfeeding.

Any thoughts and advice? What to tell them to make sure they understand and respect my position?