Okay, first and foremost, deep breath. What you are going through is rough, scary and exhausting...I have been there. My first child was sick all of the time and I too refused to leave his side until I knew that he was better and that he was with someone that I trusted enough to leave for a change of clothes. I too have been up with guilt and pure exhaustion devastated by my child's illness and why he was always so sick. Fortunately/ unfortunately he was my first and so I was extra "crazy" because it was my first experience being a Mom but I can tell you that my son is almost 7 now and is doing amazingly well. In fact, he is so healthy now that he just got over his first "cold" in over 2 years and rather than kick his butt, he sailed right through it. Literally, he had 2 ear infections, bronchitis and a sinus infection and he never missed a day of school nor did his eating habits/ sleep schedule change. This from a kid who has Asthma, a Heart Condition, is legally blind in one eye and who (over the summer) had to have his brain scanned to rule out a brain tumor. When I say I know what you are feeling...I do.
My son was 9 months old when he was in PICU with a 107 degree fever. They finally discharged him after 7 days because they couldn't figure it out and well, they were afraid that it would get worse with having a heart condition. In the end, he was home for about 6 hours and we drove to Children's at 3am only for him to break out in a rash which told us that he had Roseola. That was so scary. His fever was so high he was grey and limp. I could go on and on but the point is that I know what you are going through and while you can't see it now, your son will be okay and so will you. In the end, he will also be stronger for having gone through all of this and you have nothing to be guilty for. It's that time of year but you can't keep your kids in a bubble. I know. I tried. The wind would blow funny and my son would get a chest cold (pneumonia/ bronchitis, you name it) and would be sick for weeks only to be healthy for a short time. Now, he is healthier than all of us...well, mostly. :)
Hang in there. Try to keep perspective. It's late, you are scared, out of your environment and probably not eating/ drinking very well. What hospital are you at? As long as you feel comfortable with the hospital/ docs/ caretakers...you guys will all get past this and Spring will be just around the corner and your little man will be crawling in the grass before you know it. :) Stay focused on those things.
If you need to talk more, I am here. :) Good luck and take care of you too!
N.