Are you, perhaps:
Nemesis, the (now debunked) hypothetical brown dwarf star orbiting the sun beyond the Oort cloud.
Sometimes we play catch; / Though you'd hope it more like fetch.
Part of the hypothesis was that Nemesis' orbit throws debris from the Oort cloud into the inner solar system (catch), which can cause "problems" (we'd rather it was fetch so we could return it).
I'd be the second; an honorable mention.
If it existed, it'd make our solar system a binary star system, with Nemesis being the second after Sol.
Indeed it'd be, as if I've spent my life in detention.
As above, beyond the Oort cloud.
You'd know where, if you found the tether; / Around about which, he and I dance together.
If you could calculate the barycenter of the Sun/Nemesis system you could pinpoint its location.
Cliches away; your usual meeting need not be so verbose. / PROPERLY told, I don't even have to come close.
We could observe its existence via many means (infrared telescopes, eccentric orbit calculations, etc) without needing to actually go anywhere near it.
Intrinsic you'd have a gut full of fear; /
Ladies and gentlemen, boys and girls... Dying time's here!
Nemesis was one of the proposed causes of cyclic mass extinction events on earth...
Given me a name; / Then please explain: / Where, when and what is, / That which I'll do, / Should you ever find out: / Me, I am true.
If it truly existed, it would cause another mass extinction in a few million years.
On the hints:
"Nemesis" did not exist in any question or answer at the time this riddle was posted in 2015.
1984 (from the last hint) was the year Nemesis was proposed.
For a while, another hypothetical object, Tyche, which was "the name of 'good sister' of Nemesis", was proposed (this time a gas giant within the Oort cloud, but with similar reasoning). However, both have since been debunked as not existing ("another blunder") thanks to the WISE infrared telescope surveys in 2014.
On the title:
The dictionary definition of nemesis is "the inescapable agent of someone's or something's downfall", or in other words, "an agent destined to be someone's or something's defeat".