If you have two cats, and one passes, is it better to leave him alone, or must you get a new friend?

Originally I found one female cat. She was a stray so she had a hard time adjusting, but after she did; I decided to get a male cat. The first few days, they had a hard time getting along, but this quickly disappeared, and they became great play buddies/best friends. Yesterday, the female had a horrific accident and passed. I am confused whether to leave the male as is, or will he need a new friend to be able to cope? I don't want him to be sad, lonely, or depressed, but I also remember how big of a challenge it is to have a new pet, and don't know if that's the best answer. Your participation is greatly appreciated. Best, Cat-Woman