Relationsip questions

Today and for the last few days I have been wondering if I should stay in the relationship I have been in for the last 8 months. Is is okay to stay with someone who I know is not perfect for me just so I am not alone? My boyfriend loves me so much, but my feelings are not as strong for him. He irritates me constantly with his inconsiderate behavior, poor grammar and spelling, alcoholic drinking binges etc. He is uneducated and I am a teacher, he is not in very good shape physically and it is a turn off. My friends tell me he is not good enough for me, but at the moment I have no other prospects. I thought he was a good guy and a great Dad when I first met him, but lately those perceptions have changed the more I get to know him. I believe he has received stolen property, committed welfare fraud, and a number of other things that I find to be very unattractive. I know I should break up with him, I tried once before and it went horribly because he harassed me non stop until I ended up taking him back. Sometimes I agree with him in order to avoid conflict, but I am so unhappy. What should I do? What is the best way to let someone go easily so he does not harass me and pester me endlessly?