Should i stay with my boy friend or leave him?

iv bin wiv my boyfriend for just over 4 years and we have a 1 yr old son, i do love him but im not "in love" with him, im always thinking of other men. since being with my boyfriend i have put loads of wieght on about 6 stone, and my self confidence is at an all time low. we always argue about silly things, but im just sooo used to having him around. i just dont know what to do!!!!!! life is easier wiv him init, but its not the life i want. plus theres my son to think about. please any 1 out there with sum advice???