Please never feel bad about needing time to yourself.  (Yes, easier said than done!) It's not that you want to get away from him, but you are a separate being and you need to nurture yourself in order to be a better nurturer for Michael.

Okay, so if you want Michael to be included, ask for "the least restricitive environment" at school.  Ask that they include him in an adaptive music program where he has to fill in the blank in a song and just sing a sound or a word when he is given a cue.  If that isn't possible, ask that they teach him sign for some of the words.  Does he have a goal like, "Michael will participate in a group activity with five or more children for 10 minutes" with whatever prompts over a 1 or 2 week period?  That could mean "circle time" or it could be participation in a group song.  Now that you know Michael wants to be included, MAKE IT HAPPEN.  Have faith in yourself and in Michael :)

I can sympathize with how you feel.  It always hurt to watch when others used my son's difficult behaviors as an excuse to exclude him (and they never seemed to see the hurt I could see in my son's eyes).  I still grind my teeth whenever I hear someone say that people with autism don't have normal feelings.

Now, my son generally is more understanding of this than I, although I think even he wishes that there had been a way he could have asked us what he could have done to make it possible for him to have just been included more frequently.  Sometimes I am able to get over my anger to empathize with the teachers and realize that it was probably better for my son than the experience of going into a total meltdown on stage.  I do have a great deal more respect for the teachers who were brave enough and skilled enough to have included my son in school plays, etc. during his early years (and we never did have that feared melt down on stage).

One thing my son and I did together for awhile that helped us both to relax was tai chi.  Not wanting to risk, at first, going into a class environment, I brought a book about it home from the library and walked us through the series of movements together (sometimes literally by guiding him hand over hand style).  Over some time, we actually began to move together more easily.  Sometimes, I would play various music in the background (so sometimes our tai chi took on an appearance of just random dance sessions)

I did keep a "laissez-faire" attitude about it and refused to worry whether we did the moves really correctly or how long each session would be.  I would also initiate sessions somewhat spontaneously - which helped it to serve its initial real purpose of just allowing us both to spend time together in a relaxed way.  I just checked on YouTube and there are a number of Tai Chi videos that give some instruction of the basic movements.