Recently adopted a pair of Austalian Parakeets, one of them flew away.how can i

[lythana]

introduce a new mate(male) ? my female bird its been kind of sick or down for the past couple of weeks , the male was the active one always cheering her up. he was "singing" and playing all the time, but today he flew away. ( my fault :'( ) now i want to get a new mate for my bird. how long should i wait before getting a new one? how can i introduce them? also, can a domestic parakeet survive outside? =( i feel terrible. Thanks to all.

PS ( I don't know how old my bird is)