Why don't you introduce her to him. Invite him out with you 2 once in a while. Invite her over for dinner, etc and let him get to know her. If he knows her and can see for himself that she is not a threat, he'll stop worrying about her.
I know it can be aggravating to have an insecure partner like this and it can be stifling, but if your willing to make the extra effort to prove his suspicions wrong, maybe he will lighten up over time and give you the freedom you need.
"It is curious that physical courage should be so common in the world and moral courage so rare." -Mark Twain
