#1
Ok so I replaced the strings on my acoustic three weeks ago but since it was my first time changing strings I broke my high E string. I then found some two year old strings of the same gauge and used that high E. since I didnt want to buy a whole new set of strings. I was then tuning my guitar today and that high E string snapped out of no where.

So my question is after years of just sitting in my closet do the strings become weaker then brand new strings?
#2
Yes, if they are sitting they may become rusty. That is what most likely happened to yours. You should be able to buy single strings at your local guitar shop.

A.W