Sorry for your loss. And I'm sorry he reacted like that, can imagine that's entirely not what you if needed. But if you feel you need time to process, it absolutely more than okay to take a day off (or more). Sometimes you just don't know, don't beat yourself up about feeling that you should've done something.

Also, I feel reddit can be harsh sometimes and immediately tell somehow to dump their boyfriend. Although it does seem like a very serious and telling sign how he reacted. I would tell him how it made you feel and that it's not right and that your co-worker was your friend. He has no right to invalidate your feelings, just because he feels they're out of place.