One of my brothers-in-law, a very handyman with all the tools and know how built my first coop and enclosed/roofed yard. I worked along side him helping when he needed an extra set of hands. It was built mostly of found items/ used wood/ re-purposed stuff. When we knew we were moving to our new home he and I looked over the old coop and realized we couldn't take down the old coop and move it /re-build it because there would be no place for the hens to live for the 5 or 6 days of the deconstruction/ re construction. I came up with totally different plans for the new habitat but he was "too busy" to build it for me. I found someone else to build it but I told him to come take down the old coop after we had moved if he wanted the materials to use for another project. He said he would.
Since that time (Last September) he hasn't had one nice thing to say to or about me or my house mate. He didn't take down the old coop and I was charged $800 by the landlord for it's removal. The Bro-in-law has told my sister that I "lied" to him about the coop and he had wanted the materials . In December he was diagnosed with diabetes. Although he is still an a-hole to me he now has an "excuse" according to my sister. I cannot figure out how or what I lied about but I have not let it adversely affect me ...his problem is with himself, not with me.
Sounds as if you are suffering from a very similar problem...a long term (never easy) relationship has gone into the toilet...it doesn't mean it is your fault. Cut your losses, move on, live and learn. When we babysit a difficult relationship the other person tends to lean harder and harder on us while setting us up for failure. Do you really think you are responsible for his bad humor or behavior? Take your pain and unhappiness and turn it into energy toward finishing your coop and yard...with someone else's help.