I totally understand what you are going through. What I did in addition to blocking the couple, is to also block his family, relatives & friends. Leaving no gap to have anything peek through.

Meanwhile, try working on yourself and focus on feeling and visualising both of you together.

I can't say much because I'm still on my journey but just know that you're not alone in this journey.
Loads of people here are too and will try to help you if possible as well.

I also find it difficult to let go of the past.