Good job OP.
I have also attempted CPR and got a bad result. (On my own Dad, on an MTB ride as it happens). 14 years on and i can still remember every minute of the 90 minutes it took to get him to A&E. And it was as recently as last night that I last questionned the decisions I took on the day.
I don’t really want to dwell on this long enough to read the conjecture in the other posts, so sorry if this is largely repetition. Don’t be too hard on yourself. You did your best, and certainly a lot more than other people there. You were up against shocking odds.
You’re doing the right thing to talk it through on here, and to try to get something positive about it i.e. The first aid course. That’ll help. But don’t be surprised if you still struggle a bit. Quiet moments were the worst for me eg gym, bike etc. It’ll take a while to settle down in your head, maybe a few months or over a year. Without realising, my experience made me emotionally withdraw from life and almost cost me my relationship. Maybe others on here can advise better, but there must be some things you can do to help your loved ones understand what you are dealing with.
Once again, well done, and take it easy on yourself. Drop me a line on the email if you want to talk one to one. Chrispeeuk at y@hoo.
Chris