I guess I had accepted my fate and simply gave up.

Of course in my comment this time, I didn't put a comma after 'guess' as I didn't pause after thinking, 'I guess'! Anyway, single comma I will not put after you have overruled, but to understand odd number seems a little complicated just yet. But I guess, as an afterthought, you might mean only pairs of commas can go in between a verb and its compliment, where the contents therein, between those pairs of commas, can be left out and still the sentence sounds complete.

What mixed me up is we use comma after verb in reported speech. But that may only be for quoting what somebody guessed:

I guessed, 'I had accepted my fate and simply given up.'

My commas are weak!