How close is too close for opposite sex friends with married individuals?

I am trying to put something in perspective for myself and it has to do with an issue I have been battling in my marriage. My husband has this woman friend he text everyday, has had wine with her at her house and our house while im at work, he has went out drinking with her, he has had her bring him food while working nights, much more things of this nature have occured. My husband says it is silly or crazy of me to worry about this relationship because he married me and she means nothing to him, but to me it seems completely innapropriate. So is this appropriate or innapropriate?