["I've been with my girlfriend for years and we are celebrating our anniversary soon. I feel like I need to marry her because she's the one for me."]
Congratulations!  Do you want to marry her though?  Don't jump into a marriage because it's what people expect. If you're happy as you are, just be happy!
My girlfriend and I have been together for four years. This is my first real relationship and I feel like she is the only person I want to be with.