I’m so sorry to hear about your bunny– give the surviving one lots of love and attention, and also monitor his eating/pooping/etc to make sure he doesn’t get so stressed out that he gets sick.
I just had the same thing happen about a month ago. My surviving bunny spent about a week just seeming totally depressed, but then made it very clear that he was lonely (begging for attention more, aggressive behavior if he was being ignored, major lethargy, etc), and so although I wasn’t 100% ready for a new bunny, it seemed like he was. Some bunnies are going to want a new friend, and some won’t– you’l have to see how he’s acting in the upcoming days and weeks. I would suggest waiting at least a few weeks before introducing him to another rabbit, though, as he’s going to be pretty stressed out aready and doesn’t need the added stress of bonding.
Most importantly, though, once some time has passed, make sure to bring him on bunny dates– don’t just bring a new rabbit home and assume they’ll bond. He may not want a friend at all, or he might want a very specific type of friend– you have to let him decide. When I brought Humphrey on the first bunny date, he immediately hit it off with Otis, and after a second successful date I decided they’d make a good pair. Otis actually moved in two nights ago, and I’ve been letting both of them get settled with living in the same room before starting bonding proper.
Either way, I’m so sorry about your bunny friend, and good vibes and good luck!