How dangerous is a severe caffeine addiction?

it can be severe if you drink it everyday for many years

Caffeine is just like any other drug, it must either be not taken at all or in moderation.
A symptom of addiction is when you life becomes unmanageable because of the substance and you feel you cannot live without it.  I suggest a caffeine detox.  If you have insomnia, try exercising in the mornings, this will tire you at night, but it will strangely get your heart pumping in the morning and wake you up.  For example you might do the treadmill for 30 min early in the morning.  Waking up when the sun comes up will also help set your circadian rhythm.
I drink decaf almost every morning, however, I don't intake ANY caffeine for one whole day of every week.  This could be a solution for you too.  Try taking either one or both weekend days off of caffeine, a caffeine fast.  Your body's tolerance to it will be reset.  However, you must be aware that you could have a horrible caffeine withdrawal headache.

If you knew that your action gives you trouble for a long time, then you should stop it right? It's hard when you used to be on things for a long time and you let it go. But it is the first step you must do, to let go the thing that brings you in trouble.
Find alternative ways to avoid caffeine like substituting it with milk or tea. It's dangerous! that too much consume of caffeine may lead you to have the risk of cardiovascular problems. Having Insomnia is because you have anxiety and stressed. Improving sleep by taking 5-HTP can help you just for short days, just make sure that you also help yourself to stop consuming caffeine. Good luCk!