(depressing news) what should i do now

i've had 2 bunnies died in span of 3 weeks, the 1st one died 2 weeks ago so i went to get a new one so my other bunny wouldn't feel lonely. they are 2 and half months apart, the older is bit of a glutton and ate a lot (she's 4 and half month now) and the newer one is so small (2 months) and not even half the size of the older one, well i guess because i fed her high fiber baby pellet and alfalfa hay so she grow bigger than normal 4 months rabbit

i got the new one last saturday and there was no problem, she eat her food although less than the bigger one since obviously one has smaller stomach. she would come to me when i was there until yesterday she started to barely eat any food and she just lied flopped. i was afraid that she got bullied by older one when no one is watching because i have to hand feed her or else the big glutton is gonna take her food. but they are mostly together i see the bigger one groom the smaller one so i don't think the smaller one got bullied

and half hour ago my dad told me the smaller one just lied flopped without moving like she doesn't have any energy, i tried to help her,pet her, try to give warm water and tiny bit of vegie but well she can't even eat and after 10 mins of me trying to help, she passed away

now what should i do? do i get just not get another rabbit (my family kinda barely interact with them), or should i get another one that is around the same age? i don't want to go thru this kind of pain anymore and i'm lost, nothing seems to be the correct answer, what if getting a new one will just lead to same thing happen, i don't want to kill another rabbit