How do I handle my husband's problem?

He says that in a relationship we shouldn't trust each other as that is taking each other for granted. The trouble is for whatever reason I need to trust him to feel safe. His best friend is a nice girl who I appreciate him being able to see - i do trust him and her as they are just friends. However, he says that he would like to have sex with her to deepen their friendship as well as another mutual friend. I asked him not too. He says I can have sex with anyone I want also - but I love this man and I just don't like the thought of touching anyone else intimately. The problem is I don't know how to change and accept his needs to have sex and love with other people. He wants to be able to tell her he loves her, stay the night and have the 'girlfriend' experience with both these women without me feeling sad. I'm not sure now to think in order to make this OK. We really discussed this thoroughly - he said the worst thing I can do is say no to someone you love and that I'm treating like a possession. Like a toy that I won't share. This really is off the mark, I love this man and respect him endlessly. I love that he checks out other girls - I'd be a little freaked out if he didn't. But this I just don't know if I can manage without feeling seriously damaged. We have been married 13 years and have 2 children. We have sex most days, laugh together and go out all the time, we also work together and our kids are amazing, we are incredibly happy in our relationship. I'm so completely confused as to how to handle this one. Can anyone help me work myself out?