Porn has ripped marriages apart before ... but not like this.
TMZ has learned, one of the husbands from Season 2 of "Marriage Boot Camp" once did porn for a gay website called "Straight Guys for Gay Eyes."
Shaun Sulligan -- porn name Johnny Walsh -- shot two scenes for the website back in 2009 ... one sex scene with a woman and one solo masturbation scene.
It's pretty unusual -- the website basically markets straight sex to a gay male audience ... focusing on the man's body instead of the woman's. But hey, whatever floats your boat.
Sources close to the show tell us, Shaun's porn past has become a sore subject in his marriage and will be addressed on the show.
FYI, Shaun shot the porn the same year he met his wife Sofia -- we're guessing she's not too happy about that.