I like girls/women. I've enjoyed looking a beautiful women, beautiful sunsets, beautiful paintings, beautiful views since I was a kid.
I had a traveling job and could have had sex on multiple occasions over the years and doubt my wife would have ever found out. I have been offered quite a few "opportunities". I love my wife dearly and have since before we were married. I take my wedding vows seriously and always have. I don't wear a wedding ring on my finger because I gained weight. I wear my wedding ring between my ears. And, I see no reason to go out for hamburger when I have filet mignon at home, so to speak.
If you are concerned about your husband and this co-worker, and he invited you to be with them, you probably have nothing to worry about. Unless your husband is very sexually adventurous he is not going to try and bring you and her to his bed for "fun and games". If you are really concerned, ask for the evening off at work and go with them. You were invited.
BTW, read the book, "The Proper Care and Feeding of Husbands." You'll learn a lot about your husband.
Good luck to you and yours.