How do you know if you're with the one.

Recently my boyfriend proposed and of course I said yes. I do love him. But how do you know if this is it, this is THE person you want to spend your life with. people change so much day in and day out. Over time you're not even the same person anymore. So how do you know. And if he annoys the hell out of you 60% of the time... is it right. Are you holding eachother back from greatness?