Why do I keep having recurring dreams about an old crush?

I just graduated from high school and am in college now. I had an old crush but got over him and have not seen him in six months. Lately, i've been having dreams about him. Some will be where he's trying to get me to be his girlfriend, or him at my house or we'll be out and about holding hands. There was one where i tried calling him and his (current real life gf) answered and said to never call him again. and then the most recent one is where we got married and we were at the reception having fun and it just felt so right being there...

These dreams really irritate me and was just wondering, why all of a sudden am i dreaming of him?
Why do I keep having recurring dreams about an old crush?
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