Macy, when you wrote the start of this thread, how were you feeling? As in physically in this case. I ask because I have come to realize that a lot of my biggest moments of self doubt, guilt, questioning, and depreciation come in tangent with times my other needs aren't being met. Maybe I hadn't had my latest meal, or gotten enough sleep the night before, or gone on a good walk for a while, etc. Dealing with an addicted spouse is completely mentally and emotionally draining. You spend so much energy caring for them, you run out of energy for yourself. When your physical needs aren't being met, it lowers your defenses against those negative thoughts and emotions even further.
I definitely agree with Trailmix about making a list, lists are generally pretty great. (Who doesn't love making a list of chores, then adding chores you've already done so you get the sweet sweet satisfaction of crossing them off?) In addition to that though, make a mental or physical checklist of your needs too. When you catch yourself having those bad thoughts and doubts, stop yourself, and go through your checklist. Have you eaten? Slept? Exercised? Etc. Take a minute to reflect on the other things affecting you in that moment, and also in your moments of strength and clarity. You mentioned you'd just had a therapy session right before that post. Those can be really draining, which can leave the door open for other thoughts to sink in.
I'm not saying this to mean don't do therapy or anything. More to suggest getting into the habit of stopping yourself when you have those thoughts and doubts, and consider the other factors at play in your life. You know you're not those horrible things he claims you to be. When you find yourself doubting that, stop and take stock on yourself and your needs. Abusers take advantage of any weakness to sow seeds of doubt in you. Focus on your self care, and you'll likely see those confident thoughts also coincide with moments of health. You are worth taking care of, and keeping yourself safe and healthy.