I just told my girlfriend that she's the one
That's lovely! Why did you finally tell her she's the one?
I'm sure the two of us are perfect for each other
It's good to be honest with your partner about how you feel. You should sit down and talk to her about it and see what she thinks.
I'm going to ask her to marry me at the end of the night.
I 100% support you with this and I do hope she says yes. If she did say yes, make sure you treat her right and do everything of your power to make the relationship work so that you both can have a happy, honest relationship.