oops, we have similar issues of difficulty with our ds1 although he seems to like ds2 quite a bit. He is showing his upset at not being an only anymore in other ways, such as an extreme pottytraining regression and sassy mouth. Since he has taken the potty training thing to the point that he has now had not one but two fecal impactions, I have just started him in play therapy. He is also very sensitive in many ways (your comment about touch issues comes to mind) and so I have set up an appt with an occupational therapist this Friday to see if we are looking at sensory integration disorder type stuff.
We do the separate bedtimes, which helps and I also plan outing for just ds1 and me as our special together time.
There is a book which might be of help to you called The Highly Sensitive Child. It has made a big difference in how I respond to some of ds1's more quirky things - he is also way ahead of himself intellectually as yours is, which I think compounds his problems in relating to the world at times.
Good luck, I know it seems as if they just suck the life out of you at times. Ds1 has done better lately by having lots of time to do his own thing in his room. He really loves to write and draw and I have encouraged that and promised to keep ds2 away and give him his personal space.