K.M.
This is a tough one! If your boys haven't had a father figure for the last 13-14 years, then your bf won't become one overnight. (I assume their dad is not in the picture). You are their parent--not your bf. He can help them, talk to them, etc., but I don't think he should be the disciplinarian.
One think you said really struck a chord with me. You said, "he is unwilling to accept my bf into the family but he is slowly coming around", when referring to your 14 year old. His feelings are normal and healthy. It makes me sick when mom (or dad) brings someone new into the picture and just expect the kids to deal with it--"come around". It's not that easy. No matter how wonderful Mr. Right may be, your 13 year old and 14 year old need come FIRST.
I experienced something similar. My father passed away when I was 11 (my siblings were 8, 14, and 18). My mom went on her first date when I was a senior in high school (6 years after my father passed). He was okay, but we were very protective of our mom. My mom dated this man for 4 years. She would not get married or let him move in until my youngest sister graduated from high school and left for college. My mom just didn't think it was fair for us kids. So, my little sister graduated in June '99 and they married in July '99. I really respect my mom for not dating when we were younger (honestly, with 4 kids, a business, and a full-time job I don't think she had time!). And, she really put us before herself when she waited to get remarried. She did not force him on us, make us accept him, or EVER ask him to discipline us. That was never his job. We all have a very healthy relationship with him today and I think it's because of how my mom handled it!