Step back, step back, step back!
Yes, it may well be that you think you see a way of solving his problems for him better than he can do himself. But the success of his adult life depends on him learning to solve his problems for himself. He has 5 years to practise in before he needs to start functioning at university or in an adult workplace. He will need that practice.
When he started learning to write, he obviously didn't do it as well as you could. But you didn't snatch the pen from him and do his homework for him just because you could see how it could be done better. You knew that he had to do his own stumbling. If you were a proficient footballer you wouldn't have offered to take his place in the match because you could do it better. You let him do it, and take the risk of failing.
If he is bullied you should step in- just as you or another adult would step in if he had an accident on the pitch. Otherwise you let him take the risk of messing up the game.
The other aspect to remember is that nothing damages you socially at this age more than the perception that you are an overprotected mummy's boy. Boys are very sensitive to this; chances are that you would do more harm than good by stepping in. This sort of thing will be remembered- don't land him with a reputation that may take him years to live down.
And a third point- to gain confidence socially, he needs to believe that he is actually competent to manage his own affairs. Every time you step in and try to arrange things for him you are telling him you don't think he is. And as you are one of the people who might be expected to know him best, this will have him seriously worried that perhaps there is something wrong with him, that perhaps he is incapable of managing his own life like other people. Parents who spend a lot of time worrying aloud that their children are lonely are basically conveying the message that there is something wrong with their child's life. I have seen children who were happy loners have all their confidence destroyed by a parent going on about it.
A much better message is: "Well, friendships shift and most people go through lonely stages in life. That is normal. It can be tough at the time, but it doesn't mean anything much, sooner or later you will find new friends. I have every confidence in you."
Listen but don't go on about it- as alpinemeadow says, one of the important jobs we do as parents is to distract.