what if your boyfriend doesnt want to marry you?

I've been with my boyfriend on in off 5 yrs we r really young n during one of our break ups I had a son now where back he's a great dad to my son after two years seperated I was pregnant by him n misscarried now we have 1yr and 7 mnths he says I'm his one in only he's always gone cause he's a musician I wanna get married n he says not now every time I bring up the subject he cuts me off n we always end up n an argument he says one day but not now