I think if you’re dwelling or ruminating on the ending to try distracting yourself with other things, if readings not cutting it, then try doing something else. I often find TV to not be enough of a distraction when I’m lost in thought. Throw yourself into a project or a hobby until your mind settles a little. I had a similar problem years ago when I read The Notebook the first time, (my grandparent had passed away and I don’t know why the heck I thought it was a sensible idea to read it). It will pass, and you’ll probably always look back at that story and feel sad or mad about the ending but it won’t be as big a deal anymore.