I'm sorry OP that some PP on here are saying it was his DM wake and the day wasn't about you. That's unkind of them and they are just goading you so ignore them.
You are being left out by friends and family and some of them are being very unkind.
At the wake you should have all been together and / or flowing between people No one should have left you alone like that.
Maybe they thought you wanted to sit there alone with your DC. Unlikely but maybe.
Wakes are very emotional and people react in ways they wouldn't normally.
What would have happened if you had gone over to the table your DP was sitting at ? How did or would they have reacted.
Were you sitting alone because your DC was playing up and had to be dealt with
away from others.
I personally think there is no excuse not even a wake that your DP felt it was ok to sit with his ex and leave you alone like that especially as you did have a good relationship with his DM.
You should have all been sitting together or at least you should have had other family members on your table.
You were literally left in the corner by everyone and I'm so sorry for that, it must have made you feel very sad and alone. Which is not a nice way to feel
Is your DP normally very kind and loving when it's just you and your DC at least ?