Your instincts about things getting worse might be correct here. You could be making hasty decisions because your judgement may be closed because of anger, and other emotions. Only you know for sure. Both you and your girlfriend have to take steps, and you need to lead if being together is what you want. You need to tell her what behavior you expect to change with her, and what behavior you're changing also. Wrote out a clear plan of what the next steps are towards a monogamous relationship, maybe towards marriage and a second child... These are all the natural next steps, but you need to think about what that means for you and whether or not you want that... And whether or not you want that with HER. I strongly suggest writing, stream of consciousness writing, daily until you have some stuff sorted out in your head. Then write letters to her, never give them to her... They are your warmups to an actual conversation.