Welcome, Brenda.
There are plenty of us here who share your story and have been through the same kinds of experiences. I used to wear my wife's things in secret, but this became increasingly difficult as I put on weight over the years. She has been a size 4 petite since the day we were married (35+ years ago), but I am now a size 16 tall. After hiding in the closet for too many years, I came out to my wife and started buying my own clothes. It is so much nicer to wear clothes that fit and that are styled more for a body like mine. My wife has been very supportive and has often bought me a dress or skirt and top for a birthday or Christmas present. I would recommend giving serious thought to telling your girlfriend about your crossdressing. It is possible that she will leave you over this, but it is equally possible that she will be supportive. I personally think that the problems with hiding this from a spouse are not worth it. If nothing else, the secrecy harms the relationship between the two of you.
Louise