It's the fear of losing him... I used to have dreams like you too. When you're with someone that you truly like/love/admire you're subconsciousness reminds you how much this person means to you.
Try talking to him to confirm your feelings. Is he seeing someone else in "real life?" Joke about it. I hope he feels the same. My ex BF, who's my really good friend now, had the same dreams of me leaving him too. In fact, he had more dreams about me leaving him than I did when we were dating. Of course, he tells me sometimes that he never wants to lose me. I let him have his freedom, crazy friends, and we spoke like best friends 90% of the time. Thus, he dreamed a lot about me leaving his side. Being familiar with someone or something is key to comfort. So, I hope it's truly mutual between you and him.
Good luck.
Try talking to him to confirm your feelings. Is he seeing someone else in "real life?" Joke about it. I hope he feels the same. My ex BF, who's my really good friend now, had the same dreams of me leaving him too. In fact, he had more dreams about me leaving him than I did when we were dating. Of course, he tells me sometimes that he never wants to lose me. I let him have his freedom, crazy friends, and we spoke like best friends 90% of the time. Thus, he dreamed a lot about me leaving his side. Being familiar with someone or something is key to comfort. So, I hope it's truly mutual between you and him.
Good luck.