Yes, this sounds very similar to my ex bf who is addicted to pain meds (vicodin mostly but in desparate times, whatever he could get his hands on). Most recently he's been on Suboxone and that has caused constipation so that could also be something your husband is experiencing.
My ex had an extremely short temper, blamed me for all of the arguing, and was very defensive. I believe you are on the right track in suspecting what you do and it's unfortunate. I also understand your needing definitive confirmation to 'make a move' BUT...don't make the mistake I made which is, once knowing what was going on, thinking you have it in your power to either control the situation or even cure him of his addiction.
Read all that you can here. and if you have time, read my post "Letter to my Boyfriend". It's only going to get worse if you stay. And these are the same words that others said to me on here months ago.
Be strong and take care of yourself!