If you would like to propose to a girl with a letter, here is a simple template you can use to write a marriage proposal letter to a girl.
As we celebrate our first year, I learned that I made the right decision in choosing to have a relationship with you. We are definitely a great fit with each other from our likes to our dislikes. I love you so much and I will never be shy to admit that.
We went through so many experiences and I wouldn’t have it with any other person in the world. I am looking forward to experiencing a lot more adventures with you. With that said, there is only one questions left to ask: Will you be my husband/wife?