30 is pretty late in life to be so confused about something like this. Stay in a commitment or stay out of it. Don't mess around. People just seem time fillers to you. See where your heart is and quit all other temptations. There are words like faithful, loyal which should be more a part of our lives than "confusion," "flings" etc etc.
If you love your girlfriend, be true to her. If you don't- don't mess her life.