["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!", "I do want to marry her and I would want to do it because she's my best friend and I confide everything in her."]
Then go for it!!  Go buy that engagement ring and set up a beautiful proposal.
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.