Give him time. I think before a couple goes into marriage, first
they need to stabilize their financial status first.
We might always say that money is not important in a relationship,
but the issue is always there. He might not want to see you suffer
in the future if he doesn't have enough money to support you. But
also depends on what kind of lifestyle you want to lead. Talk to
him, don't avoid the marriage issue, find out why he has been
delaying. Find out the worries he has. If he says it is because he
is not able to provide for you, tell him that you don't mind a
simpler lifestyle (this is what I would say for I would truly not
mind, but I dunno about you).
Good luck and all the best! 
