In general, and especially for new groups, the question of what happens to an absent player's character should be answered definitively at the beginning of the campaign. What the answer will be is likely to depend both on your game system and your group, but in all situations, it's a good idea to make sure everyone's on the same page with whatever the answer is. It sounds like your group did not do this well - or at all - which led to unclear expectations for everyone. You assumed your character would not suffer lasting harm while you weren't there; the other players assumed your character was still able to be used fully regardless of consequences.
So yes, to some extent, it's okay to be upset about this. HOWEVER! This doesn't mean get mad at the other players, or do anything to "get revenge". Use your upset only to help spur the discussion of what should happen to characters whose players are absent. In other words, it's fine to say "Guys, I'm really upset that my character has been permanently damaged by choices I didn't make for him. This is frustrating to me and not fun. Can we lay some ground rules about how much our characters will do when we're not here to play them?"
This lets your group know you aren't happy with what happened, without laying blame, and should make it clear to them that your group needs a ruling here. Don't get angry, throw a tantrum, try to harm other characters, or otherwise behave badly to "get them back". Just let them see that you're bothered by what happened so they understand why this important to you.
It's probably also worth talking to your GM separately, out of game, about why this bothers you so much. Ask if there's any way the GM can do something to help rectify the situation. Maybe give you armor to replace what was damaged, or even just retcon the damage away. Make clear that you don't like asking for this sort of handout, but also that you're hurt and upset that your character was permanently damaged by things you had no control over. If you do this before approaching the whole group about the absent-character issue, it'll give you a chance to help the GM see why this was upsetting to you, and to work with them to help you approach the rest of the group.
Regarding what's normal for this situation: As mentioned above, this varies from system to system and group to group. My groups over the years have always used what we call "back-of-party mode", which means an absent player's character is considered present for all events, but idle. They do not suffer damage and cannot be used to take actions, in combat or out. Very rarely this can get weird, when the PCs find themselves in a situation where the idle character really ought to be participating, but the convenience of back-of-party mode far outweighs these occasional bumps.
If the GM knows a player will be absent, and/or the player is regularly and reliably absent (e.g., misses the third game every month due to work on-call or whatever), they might work with the player to come up with something for the character to go off and do separately from the party in those games. This is more work all around, but can create fun side-quests and help the absent player feel involved.
Some groups keep everyone's character sheets and allow another player to play the absent player's character (some systems even encourage this!). Some groups do a limited form of this, especially if the character has skills or powers needed to get through the day's game. The character's powers can be used in a limited form - perhaps the rogue picks open a lock, or the policewoman makes a call to a contact - but she doesn't otherwise participate.
There's more variations out there, as well. The point is that you and your group need to figure out what works for your game. Then, once you've agreed to something, stick with it so there are no surprises.