Good morning, Yadu. No, it is not true that a parakeet will bond only with a single partner for a lifetime. Most smaller birds, (wild and captive), may bond with another bird for a season, but during this time both male and female may be promiscuous.

There have been DNA tests performed on the broods of adult pairs and often the clutch was sired by multiple fathers and/or one male may father more than the babies of his bonded mate.

For caged birds, it is likely that a pair of parakeets that are caged together will remain bonded to each other throughout their lifetime, but given the opportunity, that does not imply that they will be 100% faithful either.