I say keep him! What is one more when you already have 3 others? I have 4 dogs (2 males- neutered, 2 females)- the only problem I have with having so many is taking walks- we have to take turns. Other than that they are great- they all get along great and keep each other company (there is always someone to play with!). Since he was raised in your household, he probably already knows all "the rules".
This may not be true for all dogs- so don't anyone take offense- but my 2 boys both seem to be way more loving and affectionate. The girls are affectionate when THEY want to be loved on ... the boys are ALWAYS ready for some attention...
