Most Helpful Girl
Even though you don't love her doesn't mean you aren't over her completely. It takes time to get over the fact that the person you use to love isn't this big part of your life anymore. You probably still need time to get over her. You know you are truly over the person when e. g. you hear a song that reminds you of your time with the person without it hurting anymore.
Don't be too hard on yourself. At the same time it isn't fair to your current gf that you are like this. Maybe don't hang out with your friend as much when she is around. And tell him that even though you and your ex aren't together anymore it's still weird when she's around so he can be more mindful in not bringing her home when you are there etc. I mean after all your best friend is going out with your ex! So he should respect your wish.
Most Helpful Guy
I'm Going To Give You My Unlicensed Professional Opinion, You Might Not Love Her But The Feelings Are Still There, If It Bothers You So Much, Stop Going On Double Dates & Stop Hanging Around Her. Your Feelings Are Still Strong & You Need To Back Away, Stay Strong & Stay Positive...