Need help explaining Sex with one is not better than the other
So my BF and I have been dating for five years now, we have always had more flexible boundaries but we completely opened our relationship 6 mounts ago. My BF has seen other girls but is not currently. I have also see girls in the past but recently I have started seeing a man for the first time. We are really to move our relationship to the next level, But my BF is uncomfortable with this. He believes my new partner will perform better sexually than him, and that I will rather have sex with my new partner.
How do I explain to him that neither one will be better than the other one and that I will still want to have sex with him?
Thank you for your help, Vera