I feel like a terrible human

I had my little boy at age 19.. He is 7 now and he is the light in my life. I simply just adore him to pieces.. I'm not with his father anymore but he is very involved in his life .. Together we have raised the most loving little gentleman. He has a huge heart <3 I don't have family where I live and I do have a lot of support from my ex and his family as far as help with taking care of him while I work.. And since we have joint custody our time with him is pretty much 50/50.. But financially I'm pretty much on my own.. For about 5 years I've worked my ass off with 2 jobs.. And still found time to spend with my son. I would get little phases when I would start dating someone new and maybe stretch the time I'd spend with new bf but really nothing major.. But for about the past year I just got tired of working so much.. I settled for a roommate and worked less.. And I started to really feel the need for alone time.. Don't get me wrong I love my son so much.. But I feel like sometimes I just want to be alone.. And I started to spend less and less time with him. Still everyday.. But picking him later and stuff like that. He has noticed this and it makes him sad, and it tears me inside to see this.. But how do I kick this phase off ? Why do I feel like this???? I know I'm being selfish.. I want to want to be a normal mom.. But it's an inner struggle to be the perfect mommy and still be young... What is wrong with me ??