How many years? Ever seriously think about leaving? All relationships are up and down, if you "glue" has been strong enough to go through 5 years of dating, marriage may not be out of the question.
Warning: Thinking you can do better will leave you a lonely old man. Everyone thinks it from time to time.
One thing is for sure: Once marriage has been brought up, one of two things will happen:
-You will get Married
-She will leave you because she wants a husband.
No one here can tell you which of those is better for you.