How do I not get one shot all the time as adc against assassins with good gap closers?

This is very fucking frustrating to me. Every time I play adc I always get one shot by fed assassins with good gap closers. Even with adcs with good escape abilities don't help me very much against it. In teamfights I'm usually near my team and poking whenever I can but assassins ALWAYS get behind us and go in and one shot me. Any tips to prevent this BULLSHIT would be very appreciated.