I'm sorry you're feeling like this Emily. Yes our lives are ephemeral but we can do positive, lasting things on the way. Things that really improve other lives.
Is there anything you'd like to do that will help others? EG walking dogs at the dog shelter, volunteering to clean out kitty litter, shaking tins at passers by in pet shops (I am a total introvert but I actually found this really empowering and fun!)
Even just clearing out your cupboards and taking the results to the local charity shop can help immensely.
Then you're no longer "That sad twat who let people die", you're "that person who gave something to less fortunate others".
We had an issue a month or so ago and my son was in absolute pieces thinking "I could have prevented this".
We ended up having a go through the cupboards and donating about £50 worth of stuff to the local food bank, which my son had used in the past. As we were tipping stuff into the collection point (Tesco) a volunteer came up and said "Well I was expecting to take this with me but I see I'll have to come back tomorrow with a colleague who can drive! Thank you very much!"
My point is (sorry I'm rambling) - helping others helped ourselves. Feeling "useful" can be a big part of feeling like there's a point to life.