A friend of mine likes to keep her boyfriends a secret from everyone until she knows that the relationship has legs. She doesn't want to introduce someone until she's sure that the relationship won't be a short one. I know other people who's parents and friends have met pretty much anyone they've ever dated. Whether it be for 2 weeks or two years.
You need to talk with her and find out why she's keeping you a secret. That being said, if you don't like being kept a secret for whatever reason - then break up and find someone who dates with a similar attitude to you.
Lastly, if *nobody* knows that you and she are a thing - be aware that she could have more than one boyfriend.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.