I think dreaming about the sun not going away may have to do with the idea of being exposed, of revealing something that shouldn't be revealed.

It could also have to do with the idea of feeling pressured to do something, constantly feeling the heat upon you.

The part about sex with your ex-boyfriend might just be your unconscious mind randomly picking your ex as someone to have sex with from your memory stores. It's quite common to dream about sex with someone you have no intention of having sex with in real life. Nothing to worry about; just enjoy the sex.

Or it might have to do with either of the ideas about the sun mentioned above.