Do you think it's ok for you SO to have a BFF as the opposite sex?

My fiancé has a shady past. He had a lot of women before me and this fool never like to use a condom. He was like a rabbit just humping away. Now that he met me he says it all changed for him and I broke his ice cold heart and warmed it up. But his fb is a bunch of females and he has 2 best friends. One guy and one girl. I don't like the girl cause she just is a really immature person and I told him before that it's not impossible for her to fall for him. Since her boyfriend isn't such a good dad and fiancé to her but my man is awesome dad and just overall loves me. I get jealous and I feel like it's almost impossible for the opposite Sex to be a bff. He said she's not attractive and is considered one of the guys. I told him it's not all looks. When you connect with someone emotionally and intellectually you can fall for them. What do you ladies think?