You’ll find me before the beginning
And at the very end.
I can provide an experience most thrilling
When you do not know what lies around the bend.
As your cloak, I could hide you from harm.
Eyes need be your only worry.
But beware! Break me and so shall sound the alarm.
I would then abandon you, necessitating you to hurry.
From time to time, I’m not bad.
At times, you and your other half may need time apart.
And while too much of me will drive you mad
I can serve as the string to sew back together your reluctant hearts.
What am I?