I've been in a similar sort of situation... it turned out the guy just wanted to use me for sex and be in a relationship with his other person, basically. And he loved the attention of 2 people.
I'd say he's saying he loves you both because he wants to be able to have both of you. Don't let that happen. If anything, I would leave him alone completely until he's less "confused", and knows what he wants. Don't just let him be with her and have you there whenever he decides he wants you.
That's probably confusing and hasn't really helped, but basically, it would be for the best to just back off at least for now I think. I know that's what I wish I had've done.