This is not a legal question. I cannot tell you whether you 'should feel bad' because i don't know his side of the story. Try to forget about him and move on with your life. Plenty of fish in the sea.
This answer is for informational purposes only and should not be construed as legal advice.
No one on this forum is going to defend this miscreant if factual. If it makes you feel better, write a cathartic letter and submit to the USCIS.
The outcome cannot be predicted, since the USCIS may disregard it as another letter from a disgruntled former spouse.
It's completely up to you. It will make it somewhat harder for him to have his condition removed, but you should assume he will be able to keep his status and eventually become a citizen.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
It sounds like you have been through and awful lot and I sympathize. If it truly was a case of fraud he should not be able to remove his conditions. Whether or not you should feel 'bad' for reporting the issue is not something that can be addressed here. It will make it harder for him to have the conditions removed as USCIS will investigate your claims and if they are found true he will not be able to remove his conditions. and could be subject to a criminal and civil penalties as could you if you were found to have voluntary purported the fraud. If you did not report it then your side of the story may go unheard.