Nether Portal Bug

Not sure if its a bug, but i built a nether portal in my house and went through it, i did somethings and came out. Then because i lived far away from my friends they built a nether portal so we could Nether travel to each other when suddenly their portal's exit is also my portal exit, are portals supposed to link to each other?

 

Something else that annoying is when i enter my portal and leave later on i come out of their portal making me travel a couple hundred blocks just to get back to my own home