Re: being upset (or not) over a wizard fireballing the party
Assuming the players are fine with it, this all depends on how the players want to run with it.
It can range from "yeah, my dude's fine with it. Magical healing and all that jazz" to an over dramatic "do it! Fireball them now, while I have them distracted! I can take it!"
Heck, you can even say "oh yeah, we've practiced enough together, this is normal" and just kind of narratively ignore the HP damage (not actually ignore, just not address it in the narrative).
The important part is "if the players are fine with it" though. If you don't have buy-in from the player you're about to friendly fire, then you shouldn't be surprised if the player and/or PC is mad at you. If you've got buy-in, you can explain it all sorts of ways.