Rabbit question!!?

i adopted 2 four year old bunnys 5 months ago they were not well socialized when i got them so they have always been timid and the humane society was chaotic. i brought them home with me and they lived in doors i fed them pellets, fruit, veggies, hay, bird seed and once the weather got warm i built a hutch for them to play outside in with a caged in area and an insulated area for the night. the girl pes away this morning and i dont know why. any ideas what could have happened? and i dont know what to do with the boy now i am sure he will be lonely. what should i do to keep the boy happy would it be appropriate to get him a new friend. he is older and anti social with humans so i dont know how he would deal with another rabbit. him and the girl were friends since birth. please only serious answers.