I’m very sorry about the loss of Pablo. Rabbits can hide their illnesses and we often don’t know anything was wrong until they have passed. Since he was peeing a lot and had smaller poops, it’s possible that he had a urinary infection, and that could have led to the beginning of GI stasis. It’s also possible that he had some unknown condition from birth, if he was a young rabbit. The only way to know for sure is to have a necropsy performed.
Since Lola was with him when he died, that gave her closure. Spend as much time as possible with Lola. Make sure that she continues to eat, drink and poop normally. If you are worried that Pablo may have had something contagious, you could take her in for a checkup, to give you peace of mind. You may want to get her a stuffed toy rabbit to cuddle with for the time being, if she isn’t a chewer. You could start looking for another companion for her whenever you feel the time is right. If you have rescues or shelters in your area, you could start your search there. Almost all rescues and many shelters will have rabbits that are already neutered, so that you could start the bonding process sooner.