(Background; My actual car is a manual and it got reversed into the other day so driving an automatic hire car)

Last night I was driving with my girlfriend back to her house and I felt a bit sick in the stomach and was just sitting in silence, I was in my own world stressing about my car and life in general - I was driving at about 80-90km/h and for the first time ever I mistakenly thought I was still in my own car and as something went into my eye I went to downshift so I could keep a bit of control and speed whilst I fix my eye and I hit the break with my left foot. In the 1 second it took to process everything and think about everything that was going on and as I was going to take my foot off the break the car that was behind me smashed into us and caused a 4 car accident.

Yes, it was a very honest mistake, it was the first time it’s ever happened and I thank God no one was seriously hurt. The car behind me seemed too close but I just can’t help being depressed about the whole situation; if I would’ve stopped at a service station earlier or been in a different lane would it still have happened? Am I the one at fault because I made that small mistake? Why did it have to happen when my girlfriend was in the car with me? Just why? I feel like everyone has the right to push me down and say I’m in the wrong and I feel everyone should criticise me and make me feel like the piece of trash I am. People keep saying accidents happen and sometimes God puts us through things we don’t understand and that they’ve done the same thing too when driving an automatic but I can’t help but feel like they’re just taking pity on me and don’t want me to feel bad when I should.

TLDR; Was the front car in an accident and I don’t think I’m at fault but can’t help but feel like I am. Just need some help on how to stop stressing and feeling like this.