My Son Is Having Some Problems. Any Advice?

This may be quite long, but please bare with me, I need some advice or insight.

He has a younger brother who lives with his father.
My two children did not have an easy time growing up, the financial situation was very difficult, so we did not live in the nicest of houses and we simply could not afford for them to have the same things as the other children and they were both bullied quite a bit, there father worked most of the time and I suffered from depression at times, so I could not always be a great help to my children, although I did try all the time, their father and I also went through a very long, nasty and bitter divorce as well, so it has not always been easy for them, better in recent years, but hard in the past.

My older son moved in with me for his junior and senior year in high school, because he was having a rough time in his old town, mostly it has been fine, since moving here he joined the LDS church on his own, he is fully active and made some friends through that.

I noticed a few traits in him, one being he has a temper, like some girl laughed at him and showed the class his low test result once and he came home in such a huff, like slamming his bag, kicking things over, he apologized and cleaned up after himself, but he was really mad, this sort of thing happens a few times a month, he is not violent with people anymore, but when he was younger he used to get into a lot of fights, most of the time though if he is angry or upset about something he won't let me know, unless I ask him, he will just sulk it out in his room, he has an attitude of never accepting help.

Something else I noticed was mood swings, sometimes he is 1,000,000% he will be active, getting things done, happy, chatting away, being productive, then seemingly for no reason he will be withdrawn and tired, some days he will do nothing, he can't even find the will to get out of bed, he won't want to talk or do anything that day.

Anyway he failed his junior year he wanted to drop out but I made him repeat the year, it had a somewhat positive effect, he is working harder and getting good grades now.

I have noticed a few other things though the even gave him a real Napoleon Complex, if anyone brings it up he will get very short with them, also he seems to be trying to take on too much to prove himself and it can't be good for him, he has learned to drive and to play piano and draw, he reads classic literature and writes his own, he has taken martial arts classes, he has been reading up on every subject imaginable, criminology, psychology, history, etc. He is teaching himself to cook, all those sorts of things, seeming to try and make up for the fact he was held back a year and if someone brings up his being held back a year, he will list all of the things I just did to prove himself.

Another concern I have is that he seems like he is quite lonely, when he first made friends in the church he used to hang out with them all the time, road trips, parties, sleep overs, etc. They were always laughing and joking, eating out, however now the other boys in the group have gone on missions, so his main social group is gone and he has not really made friends with anyone else.

He does not really speak to anyone at school, then he will come home and he does most things alone, he goes to church events, but that is it, he seems to smile through it but he still seems distant and withdrawn, as if he is just faking happiness.

I've noticed he still has a temper over some things, part of the school policy is when held back a year one has to have weekly meetings with the year tutor, and she rang me saying he is getting quite difficult in the meetings because he is getting good grades now and he has started being snappy and has requested to stop the meetings while he is on getting good grades and at the last lesson ignored her the whole time, just reading his book after giving her a sheet with his grades on.

Also in one of his classes a boy started teasing him about being held back a year and then started recording him on his phone, my son lost his temper grabbed the phone off him and smashed it on the floor, luckily school's mobile ban meant my son was not in trouble for it or had to pay for it and when asked to apologize he said quote to the boy "I'm sorry, that your mother wasn't infertile" luckily the school did not punish him further.

Firstly I'm sorry to have made you all read this Novel of a question, I'm sure you all have better things to do, but I am really concerned at the moment. Does anyone have any insight or similar experiences or opinions, I could really use some help.

Extra:
Hi guys, I did post this before but the response seemed limited, so I reposted it, but changed the original question so the forum wasn't overly spammed with one question, I also abridged this version.