Well, what I woul do if I had to end the story withouth much work is...
That they have the horrible fight. They both depart the place and I would put some Flashbacks on the backgrounds ( mixing new and old art)
The good and the bad moments.
Maybe un character dramaticly smashes the mirror and the collage of memories break too.
Then he aks himself "Is this love worth it?"
Everything fades to white they are holding hands.
And the voice says "Absolutely, this love is worth everything"
Last panel with a kiss. 
If I wanted that they don't look too "toxic" I will just ad " I'm not perfect, neither he is, but we have each other to keep learnig about life"
I understand that readers would not want a rushed ending, at the same time, it Is better than having no ending or hiatus.