Why are the dreams coming back?

After I'd say almost 6 years of on and off dating and a year long separatation in the middle of the relationship. My ex and I went our separate ways over the holidays.
Within a few weeks, I felt ok after the final break up. I had my closure, and based off the way she went about things, it seemed she had a lot of issues with some things.
I dated a girl for 4 months, but I broke up with her, because things weren't going well. At that point, I noticed that the ex of 6 years seemingly was stalking my social media. Then for about a month I would dream about her every night, and sometimes even multiple times a night, and it got me down. I hated taking a step backwards.
Then I started focusing on work and having more fun and the dreams stopped for about a month.
Now, three weeks ago, I happened to run into her again, and noticed again the stalking seemed more prominent. But the kicker was the way she was looking at me when we ran into each other.
For about a week and a half, I thought maybe she'd reach out and resolve our issues.
But she didn't.
So I decided I'm not wasting anymore time on it because things won't get resolved.
Now for the last 4 days I've just kept dreaming about her. Why? Why are they back?
Why are the dreams coming back?
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