Why has this relationship gone so wrong............?

me and my boyfriend have been together almost 6 years - we got engaged after 6 months and where very much in love. we bought a house and things where great. Then he started going out a lot more agin with his friends and me to. And now where 6 years on no talk of marriage and doing the same things. We had a few problems and have been trying to wrok things out but we keep arguing and falling out. i think i am at the end of my my tether now and possibly think we want different things. I do love him and i am scared as i am 27 and the thought of starting again frightens me, but what is the point in being unhappy. i just dont think he gets it