I agree with BarryMcguigan. I struggle with my organisation. Might sound obvious and he might be prickly to tackle but could you try find a way to tackle it sincerely and tactfully in a spirit of "I am really struggling with this, please can we try to make a plan to work it out" and "if you are finding it hard to stick to plans please can we sit down and discuss it reasonably and try to find some sort of a solution, or at least come to a workable compromise (that can be built on later)"
And also just point out what is simply blindingly obvious courtesy and consideration to you but might not be to him. It is quite weird to me how many people there are in the world who just did not appear to gave been brought up to have such courtesies ingrained in them. More often men, I speculate, boys so often get away with so much more than girls! That doesn't mean they are narcissists, pathological or vernacular - I hate so much the way that common people-things are pathologised, vilified and written off. Its decisive and negates the search for common ground. It writes people of as different and difficult and therefore only to be fought or avoided. That's bollocks. We all have our quirks and our sore spots and our blind spots. Often people are just not taught the important common courtesies that 'oil the cogs of life' as my mother would put it. It's not a personality thing, its just a thing they haven't been taught so it just doesn't occur to people. . Some people just need it explaining, tactfully so as not to create an abrasive situation. Some people need it constantly and repetitively explaining to them, again and again, patiently til the penny finally drops, and the habit of courtesy is formed.
That, I speak from observation and experience of dealing with others.
On the organisation front, or lack there of, I speak from personal experience. Long hard experience from which I am at which I am at the end of my tether. I am constantly late and scatty and disorganised and I am constantly apologising for it and trying to explain and everything. But also people are constantly irritated for me over it. Constanyly cant see why an ostensibly able person cannot do basically relatively simple things like remembering yo tell someone they've double booked, getting bills organised, getting places on time, and all the many other random mundane organising of life. I try and try, and sometimes I am so fed up of trying that I just give up and dont try, in the name of not beating myself up about it, for I am mentally black and blue from trying to beat myself into shape. Constantly apologising, and trying to sidestep the irritation of others over it, for that does become wearing. AND its often really hard not to get irritable back....... which almost always ends up recriminations. This has been a massive stress my whole life and I have worked hard to over come it. It was always seen as adhd. I had a massive nervous breakdown three years ago now, which ended up with me suicidal and landed me in a mental hospital. They took away my adhd diagnosis and labelled me narcissistic PD. This hurt, I always thought if myself as a kind and genuine and considerate person. I had hit out accidentally hurting a policeman in the chaotic few days when I was finally reaching the nadir towards suicide, so I was sent to a forensic unit by my psychiatrist, who saw me as not being sorry enough about the policeman. I was, but she saw me as a narcissist, and decided I had not expressed enough remorse. My life and mind both fallin to pieces at this point, but I should have forgotten anything to do with me and focussed on following "remorse " according to the gospel of mental healtI've now lost three years of my life to that wretched label. And my sense of self, my sense of perception of reality, any sense of confidence in my own judgement of myself, ive been through a self loathing hell, which still haunts me from time. The narcissist word is bandied around far too much, and encourages far too much vilification rather attempt to understand people, and to try to come to understandings of people and between people.
If everyone gave a bit more the benefit of the doubt and also talked to each other rather than either getting ratty or bottling it up into a head fuck.
Theres a third possibility. He's just a dick.
Gaslighting is a staged and planned thing. Sounds like this chap is being disorganised and inconsiderate, and possible lazy, whether from ignorance or intention, but I would er on the side of ignorance rather than intention, and try to gently retrain, on the courtesy front, where his upbringing clearly omitted.
Patience at this point might pay off dividends later in his training!