He was Morrissey's PA between (I think) '92 and '94. Apparently he used to be a boxer, hence Moz's obsession with boxing during the mid-90s.
They say they two of them lived together too, but that it ended in '95, reportedly due to Jake's drug addiction. The song Sunny is said to be about Jake.
Also, in '97 Moz said in an interview that he had loved someone, but that it had finished two years earlier, which would make it appear to be Jake he's talking about.
However, no-one knows if it was a sexual relationship, or whether it was a platonic friendship, as with Johnny Marr. Moz said several times during The Smiths that he 'loved' Marr, so anyone trying to decipher Moz's sexuality from the Jake era should think again!
Morrissey is also known to have had several Jake-type relationships with women over the years, so to say that he must be gay purely because he lived with Jake is wide of the mark to say the least.