OK, first of all do not get him "a friend". This rarely helps and almost always ends badly. Never get another bird unless it is solely for you because you want another one, and if you do get another bird you must be prepared for any number of possible outcomes that may result, because there is no way to predict whether the new bird and your current bird will hate each other and not even be able to be in the same room, they will love each other, bond closely with each other, and then both birds have no use for you anymore at all ever again, etc. It just is too risky and as I said it rarely, if ever helps.
As already mentioned you need to start over from scratch with him, like it's the very first day you brought him home. Clipping his wings (outermost 4-5 primary flight feathers only) can help you to earn his trust again because he will have to rely on you again, so that choice is up to you. Hopefully by the time his wings grow back in a few months you'll be back to normal with him and can leave him flighted.
Rest assured that this sudden behavior change is hormonal. It's the right time in his life for it to start and green cheeks are moody anyway, when it does start to happen they can be especially moody. So you need to take a look at his daily schedule and daily diet...What time does he go to sleep at night every day and what time does he get up? Does his schedule follow a "Solar Schedule"? If not you need to change it and get him to rise and sleep with the Solar Schedule for your area. Do a search in the search bar here in the forums for "Solar Schedule", it's by far the easiest, quickest, and most natural way to knock him out of breeding season and get his hormones to stop flaring. But you'll have to keep him on the Solar Schedule forever, or the hormones will come right back, raring to go. This Solar Schedule should allow him to get at least 12 hours of sleep every night, which is very important. What is his daily diet? Does he get fresh veggies and whole grains every day? Is he on a pellet diet or a seed diet as his staple food? How much protein does he get each day? High daily protein will also contribute to his flaring hormones...
Now to me a major red flag in your situation is the fact that his cage is in a spare room in your home, as you call it "his room". It sounds like it's a bird room you have in your home, and with some birds this setup works well, but with many other birds it can cause extreme separation anxiety or a total lack of socialization. You have to realize that your bird is off in a room away from where the action in your house is. He can here you and anyone else that is in your house, but he can't see you or the rest of them. He hears the TV, music, talking, whatever is going on but he's back in a room alone with the door shut. Like I said, some birds are much better than others at entertaining themselves and can take the fact that they can't always see their person or people. But some birds absolutely cannot take this living situation and they actually become frustrated, angry, upset, jealous, and finally unsocialized and aggressive. Hormonal periods make this all the more worse, and him being a green cheek conure makes it soooo much worse in and of itself. Green cheeks are not called "Velcro Birds" for nothing. They are very affectionate, needy birds that don't want to be away from their person or their mate if they are in a flock of birds. So I'm willing to bet, in fact I'd bet my life on it, that if you moved his cage out of that room and into the main living room, TV room, den, whatever you call the main traffic room of your house where you and anyone else that lives with you spend the most time, he will do a complete 180 in behavior within 2 weeks or less. Now don't think that you need to be interacting with him directly once he's moved to the living room, that's not the point here. The point is that your bird is not entertaining himself with his toys or whatever else he has in his cage or in that room he's been in alone, he can't do anything but focus on the fact that he isn't a part of the action in your house. So once you move his cage out to your living room you just go about your normal business. My birds are all in my living room, their cages are always open when I'm home and they only get locked inside their cages when I'm gone. Otherwise they can come and go as they please, but the point is that they are all happy, healthy, loving birds that all entertain themselves, whether in their cages, on their cages, on their playgym, etc. I watch TV, play guitar, read, I'm on the computer, etc. and they entertain themselves. They might sit on me if I'm on the couch watching TV, but the point is that even if they are locked inside their cages they are IN MY PRESENCE, ARE A PART OF THE ACTION, and can see what they hear. They're included. This is how you keep your bird socialized, people just simply walking past his cage, talking near him, talking to him just by saying hello to him as going by, people simply sitting on the couch across the room from him while he's sitting on top of his cage, this is what he needs and wants. Has he started constantly calling to you when you leave "his room"? If not, he will soon, he'll start contact calling you, which is just screaming, as soon as you leave his room. And generally they don't stop for a long time. They want to be in your presence, in the action of the home. And you can still put him to sleep at sunset, or earlier than you go to bed, and you can still watch TV, talk to people in the room or on the phone, whatever you want to do after he goes to bed (important he gets 12 hours each night). You simply have to cover his cage when it's his bedtime. The lights from the TV and the sounds from the TV, stereo, talking, etc. will not wake him up once he's covered, they sleep like a rock under a cover. He'll actually sleep more soundly and deeply because he knows you are in the room watching TV or whatever it is that you're doing, this will make him feel safe and secure and allow him to get quality deep sleep, which will in turn help his hormonal behavior. Try it for 2-3 weeks, move his cage to your main living room, get a blanket or something to cover him at bedtime, and get him on a Solar Schedule. Even just moving his cage will help immensely. You'll see a change pretty directly. And please do still try to interact with him as much as you can for as long as you can each day. You'll obviously have to get his wings clipped before opening his cage door, but that's easy enough. Then you can just open his cage and let him come out when he wants to, he can hang out on top of his cage, play with his toys, you just keep doing your thing in the same room. If he wants nothing to do with you right now just keep walking past his cage, saying hello to him when you do, talk to him from across the room, on the couch, etc. At first after you move him he'll keep to himself, play with his toys, etc. But quickly he'll realize that he's now a part of the family, a part of the action, and won't be put back into that room alone again, and he'll pretty quickly walk over to you, sit on your shoulder, etc. I promise, it works.
"Dance like nobody's watching..."