I made a nether portal, I used it a few times, made a base in the nether etc. Tried to use it, and it spawned a new portal in the nether completely separate from my original one. I went to take it back into the over and it spawned a NEW over portal 2000+ blocks away from my base/original portal. So again I went back into the nether portal and it spawned me in a random place in the nether but this time with NO return portal. Just poof, nether and no way out.... I tried to get back to my nether base coords but they were 2000+ blocks away and I didnt have the supplies to get me that far. Ended up dying... 
Nether portals not working is game breaking!!