How can I fix this problem between my two friends?

I have a situation were Im having a hard time dealing with my two friends.
(I'm going to have to make up names here)

My story is my friend Nina started to hang out with me and my friend who I hang out with a lot, Kena. Me and Nina are good friends like we have talked a lot of conversations in the past but we never really hang out because she hangs out with her best friend. Until now due to Nina's best friend who have started to replace her with some other friends and now she has no one to hang out with so she decides to hang out with me and Kena. Though my friend Kena she doesn't like Nina because of what she did to her in the past. So she starts to distance herself away from Nina. I don't want to chose between them but lately I've been hanging out with Nina because I'm not the type of person that leaves loners left behind especially if that loner(friend) was always there for me whenever I needed someone to talk to and plus Kena she has other friends who hangs out with her. But I don't want Kena to think that "of course I'll choose Nina". In the future I feel like I have to choose between which one to hang with because the other doesn't get along with the other. So how do I deal with this problem?

Thank You all for your help I really appreciate it I'm sorry it's long