I don't believe any parent has not had times when they were just getting by. The only right thing to do is whatever you need to do to make it through.
I think that saying he deserves to be seen/heard while he is upset is too hard on yourself. I have left DS1 crying in his cot when i couldn't seem to calm him down. Once i remember vacumming and the whole time i could see the baby monitor going mad, but i was not in the right place to sit down with him and soothe him. I needed soothing first. There are some mums and Dads who never seem to need help - but i reckon there are loads and loads more who would love some help but don't never actually ask. And i don't mean help with parenting - just help with dinner or picking up some groceries or a 30 minute break to have a shower or just someone to hold the baby for a while. In the good ole days no-one used to ever do this parenting thing all alone.