I dunno if we needed the presence of another girl but the threat of one might be enough. I just don't want Borra to happen because lo and behold Korra's jealous bone is showing again and she has to have what she can't have. If Borra is going to happen, it has to happen honestly and organically probably so Bolin isn't doubting Korra's legit feelings. There's no reason why he shouldn't make new friends, some being female and possible love interests but I think he has been burned to want to take things slow should he pursue an interest, he would start off as a friends with flirting. Ya know.