How do i know when it's time to break up? (if you are or were a single mom, i would love your advice)?

I've been with my boyfriend for just about 5 years now, we have a 3 year old child together. Basically in a short summary here is our story, we got kicked out when my mother found out we were pregnant (I was 17 and a senior in HS). So we have been living together every since then, supporting ourselves .. in our own apartment. It has been a tough past couple of years, we resent eachother and it has felt anything besides a good relationship for a while. I love him but I am not in love with him. I feel like I am with him because i don't want to tear our family apart for our childs sake. I also was dependent on him for a while but i just recently started working so hopefully soon i will be able to support myself without his assistance. I just don't feel any affection towards him, but the thought of us not being together and him being with someone else hurts me, beyond belief. I don't want my child to go through a hard life, I don't want to struggle ... so am I selfish for not breaking up with him, i feel like i'm just looking out for our kid. If i break up and struggle then my child won't have the best life. Because if i stay with him then i won't struggle and my child would be happy, eventhough i would be miserable. I care about him so much and want nothing but the best for him, but with everything so negative lately I am confused and to top it off I don't get a long with his family anymore. I don't know what to do anymore .. i am open for advice. If any single moms have gone through this and come out strong and happy please share your wisdom. I'd really appreciate it ..