Viewers of Thursday night's episode (16 June) saw Marco and Laura getting down and dirty in the pool before showering together naked. They previously had sex in the house before deciding to "just be friends" ... which didn't last.
Marco has claimed to have a "hall pass" from fiancée Kim.
Speaking on Big Brother's Bit On The Side, former Celebrity Big Brother housemate Stevi said: "If you have a boyfriend, girlfriend, fiancé, whatever, you can't do that sort of thing, I'm sorry. If I had done that, I would get a slap and my thing cut off! I'm not being funny, it's out of order!"
Stevi's fiancée Chloe-Jasmine Whichello added: "As a 21-year-old boy and a 30-year-old woman, they are having fun, although he does have a fiancée so perhaps it's not appropriate. But they are consenting adults. I think they should just make their minds up."
On BBBOTS, Rylan also spoke to relationship expert Annabelle Knight, who said of Laura and Marco: "They are deeply involved in this cyclical behaviour where they do something maybe they don't feel that comfortable with, then feel guilty, so they cool off, then after a drink, or 48 hours, they find themselves back together again."
Annabelle also spoke about the "hall pass" situation, saying: "I think Kim has no control in the Big Brother house so she has tried to regain a little control by giving him this hall pass. She has no say over what he does. By doing it, she's saving face should he do something. A hall pass tends to be for a one-off thing, an open relationship is something completely different."
Kim tweeted: "FYI I said #hallpass NOT open relationship. I don't watch bb, but I heard this today. Worst thing I can't even talk to him #bbuk #bbmarco (sic)."