It sounds like he was being responsible in the past but things drastically changed. I don’t think you can conclude he’s a bad person at this point or suspect he has ADHD since it’s not been a long term issue. It sounds like something suddenly triggered him to be this way, perhaps depression, stress, anxiety or related. At this point, he needs help. Some people here suggested that you leave but I think that’s your last option especially if he defiantly refuses to seek help or doesn’t follow through once he gets help.