Should i stay or should i go?

My boyfriend is a real sweetheart. He holds the door for me, pulls out my chairs, and we talk for hours.There is just two problems. One is that he is a major slacker. In the biggest sense of the word. Lately ive been working out (lost 15 pounds) and he tells me i look great nad he wants to do that to but when i try to help him or encourage him to work out he wont. Also in school he doesnt care about his grade and just takes the easy way out. He is smart enough but he just wont try. Whenever we talk about college he doesnt seem to want to do anythign with his life, weve been together for almost two years and this problem has steadily gotten worse. Its gotten to teh point here i feel more like his mom than his girlfriend. Im so tired of him telling me how he wants to do something and then he doesnt. He is very childish and even when we are having a serious conversation or im upset he jsut makes jokes aobut everything. Its to teh point where im not sure why im even staying with him. He gets alot out of our relationship, always saying "i want to show you off" and "how did a guy like me score you?" but im begining to wonder if i need an upgrade. I jsut feel so held back and he never wants to do anything or be adventures. please give me your oppions men and women. I dont want to be a cold hearted ***** i just feel...stuck in a relationship that is going to stay the same forever.