The following are some sweet copywriting suitable for young couples to officially announce their relationship together:

1. "Our story begins from now on."

2. "From now on, there is one more important person in the world."

3. "I want to tell the whole world that I love you."

4. “You are my little happiness.”

5. “Let us go through this wonderful time together.”

6. “I don’t need anyone else, only you. ."

7. "You are the only one in my heart."

8. "I want to experience more life journeys with you."

9. "I will always protect you until the end of the world."

10. "You are the only one in my heart, and I love you."

I hope these sweet sentences Copywriting can help you express your feelings and make the relationship between you and your young couple sweeter.