I cant stop worrying about diseases that will kill us, me, friends, etc. Can I get some good news on killer diseases?

Health anxiety. This is fairly common and CBT therapists are often able to help you learn what you need to know and do to manage it. You won't be surprised to hear that a consciously healthy life style is a good start. Avoiding obvious risks and healthy diet, exercise, leisure and solid relationships are all beneficial. Check into finding a therapist you trust.
Secret:Address worry. The problem with excess worry or anxiety is it can always find something to focus on. Even if there were no killer diseases, there are other threats that could draw its attention. The key is to address the anxiety. Worthwhile discussing your concerns with your primary care physician or a counselor. Note: diphtheria, smallpox, plague, & tetanus, were once widespread killers - but no longer.