Why hasnt my b/f proposed?

My b/f & I go waaaay back. We took eachothers virginity when we were teens & then broke up 1 1/2 later cuz of his dad. We went our separate ways, but always found our way back to eachother. After I split w/ my sons father, we started going out again. We have now been together for almost 5 yrs-this time-& 2 yrs the 1st time. We have lived together for 4 yrs. I have a 7 yr old son whom he treats like his own. We do everything together. His family loves me as mine does him. When we first got back together he told me then he knew he wanted to marry me but he wanted to wait until we were completly settled. But that it would probably happen in 2yrs. Here were 5 yrs later. We now have a duplex in the nice end of town. We have both had steady jobs-Ive had mine for 4 yrs, hes had his for like 10. And so I brought it up again & he said he wants to wait till we buy a house & are more financially stable. Which are good reasons. Dont get me wrong. But then we were at our friends 2 yr old daughters bday party & there were ALL THESE BABIES EVERYWHERE!! So i kept sayin, baby-I want a baby!! So we went to go have a cig break away from everyone. He asks me "so you really wanna baby huh?!" I said uggh yes!!! He said-"ok! Lets do it. Why not. Were stable now!" So I started talking to my doctors cuz I have a few medical problems. & now he says he wants to get married first. Which isnt a problem. But how come he keeps saying he wants to get married & have babies and yet he keeps delaying it? Im so confused. I love him so much & always have. Weve known eachother since we were 12! And I know its young but Ive loved him since then. I just dont understand why he says yes soon, then no not yet & back to yes!! Please help!!!