I understand it may seem like your world is crumbling down - However, I suggest you consider stabilizing yourself through breathing and writing everything out, which means, taking the moment to first stabilize yourself and make the decision of who you are willing yourself to be and if the decision is self support then, continue writing and share. Whenever there's an emotional turmoil, writing, breathing allows you see the thoughts for what they are and how they exist, even when they seem 'too much' or 'too overwhelming' at the moment - write the inner experience.
What I also did was record myself talking the experience out, the memories, ideals, future projections, expectations, etc - everything that I could Identify was 'hurting' which is all that I essentially created in my imagination in fact with regards to the relationship. This was very supportive to see/ hear myself talking it out and then making a decision to write it out, self forgive and let go unconditionally - bit by bit. I would go Applying self forgiveness for the experiences I could see were coming up as I was speaking/ hearing myself. This can come later when you are stable enough to actually realize what you are taking responsibility for as Self Forgiveness here and how you can direct yourself within this point toward a practical decision of not allowing yourself to be subsumed in the experience, but instead understand it and walk it in a supportive manner, because we know how 'hooked on emotions' we can become at times, and it's not necessary, really.
Suggest to also see this as an opportunity to focus on the relationship with yourself, your writing, the 'who you are' without a relationship and as such, establish yourself in your process here, for you/ yourself. When I had to go through this, I made one decision to simply stand up no matter what - of course, it is sad and letting go from a person you held a close contact with for a certain amount of time, however I can only say that it is in these 'bottoms' that one can really re-consider where do we stand, what do we want for ourselves, what can we practically do and as such, do it.
Thus with keeping yourself grounded with writing in a self-directive manner taking into consideration the points above, you can see this also as an opportunity to establish a relationship with yourself and as such see and realize to what extent we have made ourselves dependent on a single person as 'our world,' which is really limited and rather unacceptable when we look at how just because of a relationship with another, we are missing out the totality of ourselves that is here, unconditionally breathing and existing as ourselves, which is what is the actual life to begin to learn how to honor.
All the self support is here, share it and let's walk this process.