I killed off my whole party.

Accidentally of course.

We were playing Princes of the Apocolypse (spoilers, beware!), and were in a dwarven cave system. This was our third campaign (for me and two others, this was our 3rd campaign ever, since we just got introduced to the world of D&D) and we were at level 2.

(Sorry if I can't describe things properly, haven't got many experience with this kind of thing)

We defeated some (huge) rats and afterwards came into a room with some giant dwarven sculpture with some sacrificial things around it. Money, one dagger, gems and the like. After distributing these things a door opened and we were attacked by some humans, one of which was wearing heavy armor and was very hard to hit (high AC). When we finally managed to kill off all the enemies, 3 of us were unconscious, 1 lost more than half our hit points, as did I (5/20 hp left).

Me, wanting to protect the unconscious players who had to rest several hours, wanted to check if the coast was clear first (so I could rest too) and peeked carefully around the corner of the door from which the enemies had come. DM: "roll initiative!"... Fuck. Turns out there was some type of guard there, who told me to leave via the exit in his room.. But I couldn't since 3 of my companions were unable to move and I wouldn't leave them. Of course he didn't accept my pleads to let me wait until they were healed (which fitted better in the not-so-experienced personality of my Aaracokra than fleeing for example), and attacked. And I got knocked unconscious... So, just one person was left to fight, tried to defeat the guard, but got knocked unconscious too. DM decided (rightfully) that the guard would kill us since we were all unconscious.

And since I feel miserable. I should not have looked. Or just barricaded the door. If if if. I feel very guilty about the fact that because of me, the whole group has to create new characters, and the DM had to prepare a lot for the session which in the end wasn't going to be played... And of course the rest of the group was laughing at me and I'm gonna hear this for the next year or so (but the mood was not very good anymore at the time, everybody got a bit cranky). Which makes me feel even more guilty.

TLDR; With 3/5 unconscious and the rest less than half hp I decided to carefully check if the coast was clear, but we got attacked and everybody died, now I feel very guilty.

Do you guys ever experienced a similar thing? How did you cope with this, or do you have any tips with dealing with these kind of things?