I think you’re right. You need to make an appointment. Fortunately, you’ve had a positive experience in treatment before. There’s every reason to think another “chapter” of therapy will be helpful. I encourage you to follow your own instincts about getting the help you need. The love for your girlfriend, and your healthy desire to live differently will help you stay motivated.
I can’t tell from your description whether you have BPD or not. There are a number of diagnoses that include difficulties with anger management and the list of symptoms you describe. BPD is the most common to meet those criteria but certainly not the only one to include unstable relationships and emotional dysregulation. I encourage you to get an evaluation by a qualified mental health professional. Whatever the diagnosis, an evaluation includes recommendations for what are the most promising treatments.
I wish you well.