These lessons also apply to loss through divorce or separation.
The most difficult lesson for me was to allow myself to feel the grief and the pain. I became an expert at filling my life with distractions (luckily, healthy ones, but distractions nonetheless). I was afraid that if I let the feelings in, that they would become a tsunami, crushing me under their power.
I had to make conscious decisions in the beginning to let myself feel some of it. My mind acted like a seawall, allowing some of the wave through, but holding part back. I was able to feel and process a little at a time, so that no one experience was too overwhelming. This piecemeal approach takes time, but it has worked for me because it breaks it down into manageable chunks, whereas the whole would be too much to bear.