Hi op, I have a nearly 8 month old and I have had almost exactly the same experience as you!! You are doing so so well pumping so much with another child too I struggled so much with just my baby!
I wanted to stop pumping from the start but kept on telling myself just one more week, I'll get him to 6 weeks I'll get him to two months etc and I actually managed to keep going till 6.5 months!
But by then I was only doing 3 time a day (once first thing while he played on his mat, once during a daytime nap and once just after he went ot bed) so i got a total about half a bottles worth from 4-6 months. I read online that even a table spoon a day is really good for them so I felt like it was worth it (and I had all the same guilty feelings about not being able to breastfeed).
I was considering stopping before my abroad holiday this summer but was feeling guilty like you, I felt it wasn't a good enough reason to stop, but a couple of weeks before that on a remote Uk holiday my breast pump broke...I got a manual one from boots to tide me over til I got home as I had a holsital grade one there but didn't get much milk out and when I got home I could only get 20ml out when I pumped so I called it a day there.
I have that last 20ml in the freezer I'm planning to have it made into breastmilk jewellery as a memory!
My advice to you if you're going to stop is first of all build up a freezer bag stock of breastmilk, this is what I had planned to do and didn't manage- you can save this for when your baby is unwell or for when they start nursery and they will get all the food immune antibodies to fight those germs then. Or you could give baby one bottle a week etc for a while, so you can spread out that goodness.
You also have the option to just cut down gradually and do it 2-3 times a day then 1-2 (supply will drop but you'll still get some)
Now that I'm not pumping omg I feel like a whole new woman again I can actually do stuff when he naps other than pump or clean pumping parts, I'm able to do my Physio exercises, he did not notice any change he's now eating solids so getting extra nutrients from there- you deserve this freedom too op especially after doing so well for three months ! I don't feel guilty - the pump breaking kind of saved me from that - but equally I COULD have gone onto a mega strict schedule of pumping 8 times a day to get supply back up but I chose for me and baby to enjoy summer exploring our world and playing together instead and I don't regret that at all x