Just like with a physical death, in the first year of separation you should be given a ‘home free pass’ to only be at 90%, or on some really bad days maybe down to 70%, of your usual competence. That is across the board from work, to friends, to home. Don’t be embarrased, turn right into this and talk to the boss and coworkers.  Explain you are not making excuses.  

I have told many corporate executive clients who’ve whined about an employee not being fully up to speed in the first year of a separation/divorce: Don’t worry your turn will come – marriage, parent death, whatever. In the real world it all goes around, so be patient, and ask coworkers to pick up some of his slack. Their turn will come too. Usually that makes sense to them, and they adapt. The whole team adapts. Then when their turn comes to grieve, that appreciative guy will be glad to pick up some of their slack.