I think your friend touched a nerve because you feel guilty about not being able to give them a friend. However that doesnt mean that your rabbits are unhappy, they are indoors so get more attention than they would outside, and as long as you put aside plenty of time to play with them everyday, that is acceptable. I believe single house buns can be happy without a bunny friend, although I do think that they are happier with one.
I dont know much about this as I think your buns were already single when I joined i think, but I imagine you have tried bonding them and it failed? If so, and if you have tried both the gradual and the short way of bonding and it isnt going to work out, then you are better keeping them apart, they are better apart than together.
Something to consider may be whether you could afford to get a rescue to try and bond your two into a trio with a third bun, on the understanding that if it doesnt work out you dont keep 3rd bun. Or perhaps get the most 'lonely' seeming one a friend, or both. Both options would enable you to keep both buns and allow you to have a friend for them.
edit: I think the fact that you are considering changing things for their benefit shows you care a lot. But your friends idea of getting rid of one bun but keeping the other single anyway doesnt seem logical. If they are going to be single anywhere, it is best they are single house bunnies with someone that makes sure they get enough space and the right diet and plenty of human attention.