When people fall in love, they often use many romantic ways to keep their love fresh. Such as write a love letter is a common way, it is simple and realistic. If you want to make your boyfriend happy, try to write a letter for him. He will feel your crazy love. 
To:My reason for living
Hello, my love. I hope you perceive all the happiness I transmit to you when I write this letter when you read it, and I hope it makes you happy.
I could not finish this letter if I described all my love for you. Words would not be enough. Just thinking of you makes me write this.
I know I will never love anybody like I love you. I would do anything for you and I only want to spend time with you. You are my reason for living and my great love.
My most wonderful experience is when you kiss and hold me because I feel so love and taken care of. Expressing our love with sweet words will make it grow even more.
You have my word that I had never felt anything like this for anybody before, and I am very happy that you are my boyfriend. I hope this letter makes you understand how much I love you and think of you.
Carolina