Good advice above from Noodles...There's no way to know if the "hitting" episode is playing any part in this, but honestly I doubt it, as you stated that he basically forgot about it and went back to normal very quickly after it happened, which is pretty typical. Things happen, and when little accidents like you described happen only once, it usually doesn't cause you to "lose their trust"; if these incidents keep repeating, that's when they start to fear you. I think this is mostly due to him going through puberty, and Green Cheeks do get extremely moody when they are hormonal, more so than a lot of other parrot species.
It's honestly just a patience thing...You mentioned something about wanting to "hand-feed" him again, I hope you're not talking about possibly feeding him formula again by-hand, I'm assuming that you were just using that as an example of a bonding activity. But just in-case you actually are thinking about hand-feeding him formula again, the answer is a big NO to that one, for a number of different reasons, the biggest one being that at his age and with him being hormonal, not only will trying to hand-feed him formula again not help the situation at all in any way, but it will actually make it much, much, much worse, as he doesn't want to be handled at all right now. Hand-feeding baby birds does not make them tame. This is something that a lot of people just don't understand, but it's not the act of hand-feeding a baby bird that tames them to humans, it's not the food/formula or the act of hand-feeding them that does this, but rather just the handling/personal interaction with humans that does it. Plus, when you are hand-feeding a baby bird, you're removing them from their parents and completely removing them from any other parent figure that's a bird, and replacing them with a human. You cannot recreate this now with a bird going through puberty, that ship has sailed. Plus, formula is not at all good for adult birds unless they are going through a medical/health issue that requires it. So cross that one off of you list, as it will only make things worse for you...
This is just going to be a time period where you're going to have to be very patient with him, and you absolutely must go at HIS PACE, not your pace. And that's usually the hardest part of this for people, as they want their cuddly little baby back, and they try to rush it, they try to do anything and everything they can to rush their bird's through the hormonal periods, and in the end, all they do is make their bird afraid of them and not want to have anything to do with them when the hormonal period has passed. You need to respect his space, respect his wish to not be "cuddled" right now, keep talking to him, keep spending the same amount of time with him as you always have, keep allowing him out of his cage just as much, the only difference here is that if he doesn't want to be touched then you need to respect that.
What you can do is what Noodles described above, which are different things to help him get knocked-out of breeding season a little more quickly. Those things include putting him on a very strict "Natural-Light" Schedule, meaning that the cage he sleeps in must be in a place where he can see the natural sunrise an sunset (light changes in the room, through a window)...And he needs to be able to see that the sun is setting, and then put to bed at sunset (best to cover him at that point if you don't already, that tells him that it's time to go to bed now), and then uncovering him right as the sun starts to rise, so that he can see the light changes during sunrise. This not only helps to stop the hormones, but it also ensures that he's getting enough hours of sleep every night, which helps tremendously with hormones and mood swings.
Also, make sure he does not have access at all to any small, dark, warm places (no boxes he can get inside of, no tents/huts/hammocks/beds of any kind, no going underneath furniture or anything else that creates a small, dark space, etc.). And no access to anything that can be used for or confused with "nesting" material, such as bedding, wood chips, blankets, towels, shirts or clothing, etc. Lots of exercise, lots of healthy, fresh veggies, lots of calcium (getting him a mineral block is a really good idea), and limit treats/junk food that has fat, sugar, etc., as these are "comfort" foods, which can also trigger nesting/hormonal behavior.
Was he DNA-tested and confirmed to be male? If not, you might want to think about spending the $20-$30 to do so, as if he continues to become so hormonal during breeding-seasons, and if he happens to really be a female, then sometimes this can cause issues with chronic egg-laying. So it's a good idea to know for certain if that's something that you're going to need to be aware of, and with Green Cheeks only a DNA-test is going to tell you the sex for certain. I think it's always better to know and be prepared for any eggs than not, as egg-binding is 100% fatal without medical intervention if it happens, and the best way to avoid a female becoming egg-bound is by providing them lots and lots of calcium with a cuttlebone, mineral block, and egg-food. But if you've had him DNA-tested and he's definitely a male, then that makes things a bit easier and less stressful.
This will pass, I promise. What you do need to remember is that your bird can sense that you are frustrated and upset right now with him, and this will make him upset. They can very definitely sense our emotions and what we are feeling, and it's best to just keep acting normally around him, and to help him get through this, rather than "fighting" it, because that is only going to stress him out more, which in-turn keeps the hormones raging. And as Noodles already mentioned, cuddling, snuggling, hugging, and holding your bird while he/she is in breeding season and is extremely hormonal is not a good thing to do anyway, as it is going to keep triggering his hormones, and if he's already bonded closely with you and you start cuddling/holding/petting him, this is going to get him all hormonal, and he's going to want to start trying to mate with you, and when he figures out that he can't, this tends to really frustrate them and cause horrible moods that he's going to then take out on you, often by biting/attacking you. They very often try to mate with your hands or your neck, or start masturbating on their person that they are closely bonded with, and the best thing you can do if this happens is to simply put him down on the floor or on his cage as soon as it starts, and then walk away and give him some time to calm down again.
***Lastly, it's very important that you don't ever scold him, yell at him, or punish him because he's hormonal, as this isn't his fault, and you'll only confuse the heck out of him and this can cause all kinds of psychological and behavioral issues. Like I said, if he's on your finger/hand or you shoulder, or even just near you and he starts to try to masturbate on you, or he does "heart wings" for you and starts a little, quiet kind of constant chirping while he's doing the "heart wings" (they drop their wings and allow them to hang really low while they're trying to figure out how to mate with you or get you to want to mate ), you don't want to scold him or anything, you simply want to put him on the floor or on his cage/stand, and walk away for a few minutes and let him cool-off. He should be coming out of this very soon, you can't rush it, just try to be supportive and understanding with him and don't let him sense that you're frustrated or upset.
