Scared

Idk why but I always feel like something in my life is missing. I’m 19 years old and my boyfriend is 20. He has a very serious job and an apartment already and is already trying to settle down. We fight almost every other day and then makeup and he always tries to make up with sex. He said that making up with sex was how it was in his last relationship that lasted 5 years. He also talks about her a lot and she even tries to reach out to him. I also try to be open to him for conversation about anything and everything but I just can’t seem to get over the fact that he may or may not be over his ex. I am also scared that I jumped into this too fast but I do know that I’m going to marry this man. I just feel that we need to talk more. Any advice??