Sounds like you're subconsciously comparing your ex to your current fiance, b/c you miss your ex? Maybe you feel like you had a better connection with your ex than you do with your fiance?

If it's been 4 years since your relationship with your ex and you're still dreaming about him, it's because you have unresolved feelings about that relationship or about your ex.

Do you compare your fiance to your ex? Does keeping your ex in your life, interfere with your relationship to your fiance?

Here's a good list of 10 reasons why we dream about an ex. There are droves of articles online about it. Hope this helps.

10 Reasons You’re Dreaming About Your Ex and What it Means

1. What stands out to me about this particular ex or our relationship?
2. Is there anything in my current life or relationship that seems similar to this former ex or relationship?
3. Is there a lesson I learned from that particular ex or relationship that I can apply to my current life or relationship?
4. Do the actions or circumstances in the dream seem similar to any of my current circumstances?
5. Do the emotions or thoughts I had in the dream relate to how I feel or think about anything in my life or in my relationship right now?”