My boyfriend is going to get on a plane to go abroad soon. What kind of short message is good?

Not a boyfriend? What are you afraid of?

If it is because you are not familiar with it, you can say, "It is rainy season now. Remember to take care of yourself outside, rest more, and don't catch a cold. I don't want to cook ginger soup for you when you come back. Hehe, liking someone is the sweetest time. I envy you and wish you all the best.