The former Spice Girls singer filed for divorce from her husband of 10 years last week, citing irreconcilable differences, and the producer's sibling, Jeremiah Stansbury, believed the pair's reported decision to invite other people into the bedroom sparked feelings of jealousy.
He said: ''Everybody has personal issues, we're all human and nobody is perfect and I'm not here to throw shade on Stephen but basically what they had going on was a very fun, loose, open kind of relationship.
''It been publicised, this isn't news from me. They liked to bring a stripper over and have a little fun and stuff like that.
''I'm only giving my opinion here, if you're not a very mature person and you're not very solid if you're gonna look at that as a license to do whatever the hell you want, then someone is gonna feel unappreciated.''
And Jeremiah believes the relationship ultimately broke down because Stephen ''probably'' didn't realise his wife - who has five-year-old daughter Madison with the movie executive, and Phoenix, 18, and Angel, nine, from past relationships - was unhappy.
Speaking to Australian radio hosts Kyle Sandilands and Jackie 'O' Henderson on Tuesday (28.03.17) morning's 'Kyle And Jackie O Show', he said: ''He's not a bad guy by any means but he can be a little rough around the edges and he wasn't probably picking up on the signs that Melanie wasn't quite happy...
''For them two it was just small stuff it was the fact that they needed to get their egos involved and argue about little stuff instead of compromising.''
Jeremiah used to live in the US home belonging to the couple, who are both 41, but left after falling out with his brother, who he claimed repeatedly ''embarrassed and disrespected'' him.
He said: ''I got kind of fed up with it because all this fame and money was going to Steve's head and he was blatantly cussing me, embarrassing me, disrespecting me. Even Melanie picked up on it, she came to me and said, 'Yo what is going on with this?' ''
But after giving interviews following the marriage split, Jeremiah claims to have heard from his brother, who has threatened him to keep quiet.
He said: ''He started sending me emails saying he is going to ruin my life that he's on to me. He has been living in a little fishbowl of his own creation for 10 years now ... Steve is just looking to point the finger at whatever he can.''
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