Just a few questions. Please take a look?

Alright, before I even start, I'm going to tell you that I'm only sixteen. Don't worry, my boyfriend (who has ADHD) is sixteen too. You see we're still in high school. Now, before you tell me that I have no business posting here, I'm not here to act like a child. I truly want to be there for my boyfriend and understand the way his mind works. I hope you don't just respond with 'you guys are too young to have any real feelings for each other'. We've been going out for a little over a year and have never had sex so we're obviously not into the whole "ignorant, hormonal teenager" thing.

Anyway, here is some background on him. He is medicated and has been since he was about four. He is extremely intelligent but his lack of focus interferes with his grades; they range from A's to D's (no failing grades though). Most of the time he is the sweetest, funniest boy in the world. ADHD actually runs in his family through his dad's side and there are signs that his younger brother may have it.

Now for the problems/what I'm curious about.
1. He has these, I guess you would call them ticks. He has this thing where he shreds wash clothes and plays with the threads and he'll carry wet paper towels around and twist them up. Sometimes he'll get in trouble for making a mess with them so I thought giving him play dough would help. He tried it but it just didn't take to it. Is it normal for someone with ADHD to have this type of compulsion? Or is it just a personality trait?

2. He also has a habit of accidentally 'lying'. It really is an accident when he does it though. Its like, when he tells me something that happened, it completely leaves his head. So he makes up the details that he THINKS happened. Then when he goes back and tells the story again, and he actually REMEMBERS what happened, everything is totally different. The first few times this happened I actually thought he was lying but then I realized what was really happening. Is this common issue?

3. Now, the most important thing. Most of the time he can laugh and joke about having it, but sometimes he just gets so down on himself. Sometimes, he gets in this mindset that he makes mine, his family, and his friends lives miserable because he gets hyper or talks too loud. He thinks everyone hates him or looks down on him for something he's trying his best to control. I try so hard to help him see how untrue all that is but its like he gets stuck in this hideous dark place and I have to fight all the negativity to pull the real him back out. Is there anything I can say or do to, I don;t know, make it easier on him?

Well, that's it I guess. If nothing at all I need is the last question answered the most. I care about him so much and all I want is for him to be happy. I think to be the best girlfriend I could possibly be, I have to do this. I feel like just putting the effort to learn more about ADHD can show him how he is more important than the so called 'problem' he has. Because, honestly, I don't see ADHD as a problem. Not in the way that people usually make it out to be. He is just a normal, loving, teenage boy. He just happens to have trouble paying attention and staying calm. That doesn't make him any less human. I just need a way to show him he is no less amazing than anyone else.

I would love and appreciate any help at all. Thank you.