You have to ask her if the other guys know she's fucking you, if they do not then it's not meaningless sex.
My wife has a friend who comes to town once or twice a month, he knows I know, his wife knows, my wife and I know his wife knows...everyone is ok with this. He's huge, goes forever and is the best physical sex she's ever had.
Once a week my wife goes to see her parents, spends the day taking them to appointments and the like. She drives an hour to get there, and goes to see this ex-boyfriend around 6:30 in the morning and stays until he leaves for work around 8:30. She gets back to his place around 7 at night and spends the night leaving around 8:30 the next morning to come home well after I've left for work for the day. He's always been in love with her, says the worst thing he ever did was loose her. He knows and accepts that she's never going to leave me, but he's OK just having sex with her. He thinks I don't know, he thinks she's cheating on me because he's such an incredible lover and she can't go a week without his big cock. Yes she's fucking him because he's better then me....huge, can go 100 times a night and the second best physical sex she's ever had. She lets him believe she's cheating because she know he thinks it's much hotter that way.
Both of these are meaningless good sex for my wife, but the second guy...it's not meaningless, he hopes some day that it's more but he accepts that it may never be more.
The key here is that YOUR other guy may be more then just meaningless sex, and if he is then his knowing (like my knowing) is what makes the sex with you meaningless or meaningful.
