The reoccuring dream

So..I have had many dreams of one of my ex's on different occasions with the varying content. It usually is about us spending time together and him doing really nice things for me. We laugh, talk , and have a great time together, which when I wake up makes me grumpy to think that in my dream, he is not like he is in real life. AT ALL. Yet, I continue to dream similar dreams of him. The most recent one, last night, we were hanging out and cooking together. He was being really attentive, and funny. There was chemistry too. I just remember waking up with a pissed off feeling that why cant dreams be real life representations of the people in our lives? But, then again, then dreams wouldn't be so interesting..I guess what I am also pondering is why he comes up so often in my dreams..and why I am so happy in my dreams and then wake up with the direct opposite emotion.