How do you know you want to spend the rest of your life with him?

Me and my boyfriend have been together for 6 years... We were doing long d at the beginning and we moved in together 3 years ago. He comes home every weekend. Until recently he is now living at home full time.  We also got engaged 8 months ago. I'm having doubts. How did you know you want to spend the rest of your life with your man? He has always been a very quiet and passive man, and I find that I'm doing most of the planning of our vacations, weekends etc and I'm getting tired.  I'm starting to have doubts about whether this is the life I want and if he's the man I want to be with for the rest of my life.