I would love to be able to help. Unfortunately this is like an algebra problem with too many unknowns. I can tell you this much for certain. There is a perponderance of evidence that you were following too close. Some might say after a green light collision like this that people shouldn't stop in the middle of an intersection with a green light. But what if that motorist saw a problem ahead? example: a stroler rolling out into the roadway... He has to stop right? Under ANY circumstance, when we can't stop soon enough and make contact with the vehicle ahead of us, it's following too close.
Others have already commented on riding technique issues that I won't rehash.
I'm not a medical professional, and only a brain specialist could tell you if the collission was proximate cause to the bleed. I beleive with the information provided,,, probably since people brains don't normally just start bleeding.
If I were your wife (dude, that's odd to say) I would probably demand you pass an advanced course with flying colors at a bare minimum. Coupled with the approval or opinion of the doctor that a future such collission would not kill you. Wives are funny that way.
On the ETOH issue that someone previously caught onto; I'll bet if you had been drinking you would deny it. So, only you know that. If so, you probably wouldn't listed to someone close to you so take it from a total stranger. No alcohol at all if you ride again. Because next time the person with a brain bleed might be a little kid who was just standing there doing what kids do. ETOH plus Fatality = Vehicular Homicide and in most States its a 3 year minimum for the first time...
I hope you take all of this in a positive way. That's how it is meant. Ride safe!