I think the 5 month mark was when i felt exactly the same as you. Youv'e been given some good advice here already, even an hour off on your own, for a facial, or a leg wax/hair cut, anything that's just for you will make you feel a hundred times better.
I remember the exact same conversation with my dh about him being so lucky to get to go out to work too, and it makes it worse when dh thought i was the one who had it easy. It was the feeling of not being understood that made it all the more stressful. You are probably at the peak of stressfulness at the moment.
Soon dh will have to take over for an afternoon (make it as soon as ds is eating anything!) and he'll understand a bit better.
The main thing is, that by 7/8 months i found the tables had turned. My DD started to be much more fun, and the whole full time carer thing becomes much easier.
Anytime i got fed up bf'ing i would say to myself, i'm going to give it up, and would think through the implications, (learning about formula, getting up to make bottles, the bottle stuff filling up my v.small kitchen etc.) Before you know it, he'll only have a couple of feeds a day, and you'll love the chance to sit down for a cuddle. (I bf'd my dd for 16 months!!)
Slowly, you begin to get more and more time to yourself, and when the day comes that ds is napping contentedly and you have your feet up doing your nails with Oprah on the TV, make sure you take note and enjoy. (And don't mention it to dh!)