Ice cream is fine... buy hey, why not eat a healthy dinner first? Small actions to take care of yourself like a healthy meal might not make you feel better right away, but they will make you feel a little tiny bit better. If you keep doing that stuff it will add up.
I'm pretty sure my relationship is over now, and I am facing much the same situation.
I've been focusing on sticking to good habits: getting up and making a gratitude list (even though it can be fricking hard to feel thankful right now), doing the dishes, eating some breakfast, taking a shower and getting dressed, doing some work, taking a walk and getting outside, playing my drums, and doing yoga before bed. It's not exactly easy because I just feel awful about things, but I know it helps if I can force myself to just take care of myself.
And in between, crying my eyes out. I actually googled 'why do we cry?' the other day. One interesting thing I learned that we may cry to get over being upset rather than because we are upset. Maybe it really is healing. Heck, if that's the case, I should be better than new soon with all the crying I've been doing.
Also, journaling to process the feelings and find some form of self-expression. Hot tea and curling up with a blanket and a good book.
Also, try Googling 'A$$hat', click on the image tab and look at the images it brings up. It's good to laugh a little.