Managing the pain is sometimes harder than the pain itself - you're already dealing with the sting of being left out, why internalize and negatively self evaluate? So you were left out, you can't surely say for a good, bad or what type of reason and so, I suggest being a bit nicer with yourself and entertain the multitude of reasons that aren't negative.

Imo, it's a workplace setting and should be treated professionally. I would carry on and direct that emotional investment into something that has growth potential.

Edit:formatting