Hi. Welcome. I am a Licensed Master Social Worker with more than 20 years experience working with individuals and families on a variety of issues.
I can hear your confusion and your dilemma, but it sounds like you need to honor that ambivalence. Marriage can feel scary but even with a bit of fear there is less trepidation than I hear from you. Meaning that even with some normal fear and anxiety
associated with it, there is still a strong desire to marry the one you love.
I hear from you that the fights and her "ways" make it difficult for you to want to make this next commitment. I hear your love and care for her too which is why you miss her when you are apart, but the "red flags" you see should not be ta***** *****ghtly. Marriage does not fix these issues so to enter into a marriage when you have a lot of reservations could be a tough space. I hear that you are long distance from one another so my suggestion of getting into some counseling seems too difficult. If you were in the same place I would strongly suggest counseling so you can have the space to look at the issues and the dynamics between you. Is there a way for this to happen?
If you decide to end the relationship there will be pain as all endings bring these emotions up. I would suggest paying attention to your gut here. If you have reservations then do not take that step at this time. There is no rush here even if you feel that pressure from her. Take a step back to really figure out your feelings and desires and if this is the woman you want to spend the rest of your life with. This is the question to ask yourself. If you know unequivocally that she is the one to be with you forever then proceed accordingly, but if you don't feel it is her, then honor that and be open and honest with her about your feelings.
Any ending can be painful, but that is not a reason to stay in a relationship or enter into a marriage in order to prevent those feelings. Dig deep here and truly see what you feel, want and desire. When you do then your answers will be clear to you. I don't hear a selfish person as you say, I hear a man who is confused and that is okay. Go easy on yourself.
Honesty with yourself and her will guide you. Please let me know your thoughts and if I can support you further.