John Travolta Sued By Alleged Gay Lover -- I Never Agreed to Keep Secrets

A former pilot who claims to have had a secret gay relationship with John Travolta is suing the actor ... claiming he NEVER signed a confidentiality agreement that would stop him from talking to the media ... but Travolta's camp says he's completely full of crap.

The man behind the lawsuit is Doug Gotterba -- who claims he served as Travolta's pilot from 1981 to 1987. Gotterba made headlines recently when he reportedly spoke to the National Enquirer about his "steamy affair" with the actor.

Gotterba does not go into detail about his personal relationship with Travolta in the lawsuit ... but says after the media tidal wave that ensued, he received a threatening letter from Travolta's attorney Marty Singer.

In the suit, Gotterba claims Singer threatened to sue him for violating a confidentiality agreement he signed when he stopped working for Travolta.

Gotterba claims he DID sign a termination agreement ... but it didn't include anything about confidentiality. Therefore, Gotterba says he did nothing wrong ... and should be allowed to talk about Travolta without fear of a lawsuit.

But Singer tells TMZ Gotterba's lawsuit is "ridiculous" ... because he DID sign a contract that contains a confidentiality agreement ... and he even included the document in his lawsuit.