My take is if your SB will bang you just to for the fuck.  She had her own place to do it at, then she had become a mistress.  If you are still looking for a place (hotel) and giving her cash then she is a SB.  

...as I am not married and the closest I've ever been to having a mistress was when I was dating the flute section in my college marching band.  Yeah I know.... "Band Nerd" and all... but go re-watch American Pie and tell me you wouldn't have banged Alyson Hannigan and 3 of her besties when she was 19 (not to mention Shannon Elizabeth!)!  
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Anyway it seems to me that a mistress would feel much less constrained to adhere to the standard SB conventions of NSA, discretion, and separation of church and state (aka: married life and sugar life). An SB enters with the explicit understanding and agreement that you are married and she will (probably) not want to threaten that, lest she lose her sugar.  A mistress will, IMHO, be more likely to think you love her more than the wife (which you might) and that you ultimately will dump the ball and chain for her. She may even decide it's worth the risk to force the issue by sabotaging your marriage in various ways. After all, she's not risking an income stream, but she could win the "big prize" of getting you AND your bank accounts. If she fails, she just goes back to the pickup bar where she met you and tags another wealthy-looking slob.  
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It seems there are a lot more TMZ/National Enquirer stories about mistresses busting up a relationship than a sugar baby.  That's not scientific, but do you really want to be a headline on TMZ?

I have had both. However, a mistress is likely to involve at least some strings attached.

The first, and longest lasting arrangement I had (over a year) was with a woman who was so great that I simply couldn't afford "exclusive". We liked each other a lot, but she needed a certain standard of living, and my wallet wasn't that big, and,  in truth, we both wanted variety, so we settled on an arrangement that let us see each other steadily, and a lot, but it wasn't exclusive, which sort of defines "mistress".

Once we worked out the arrangement, I emailed her saying how happy I was to have all that settled, and "The thought that went through my mind today was.....Mistress? And then I thought, well, time-shared Mistress, at least." And, she emailed back "OMG. Time-shared mistress. I love that so much!"

In the end, I wouldn't worry too much about the labels. Just enjoy what you're doing.

These are pretty vague categories to begin with.  I think people will disagree on how to define them.   Everyone is, of course, free to define the terms the way they wish ... it just makes talking about them with others harder.

I'm gonna just use the terms interchangeable.  But to me "baby" has a sort of age difference implication, whereas mistress has a more mature ring to it.  But that's a poetic distinction, not a technical one.

and also meant that you would be 100% responsible for her upkeep and maintenance. I guess I got that idea from reading novels where the rich guy kept a girl on the side.  Since I've never wanted one that dependent on me, I've never sought a mistress, even if I could afford one. But like Xray, I have always thought of my pros and SBs as my time share mistresses. They are mine when I'm with them, which is all that matters.  The other guys they are likely seeing are all helping me continue to have access to her by supplying more of her financial support which keeps her active in the hobby.

Sugar Baby = Sugar Baby
Exclusive Sugar Baby = Mistress
Very non-exclusive Sugar Baby = Pro

-- Modified on 1/3/2018 9:00:45 PM

The only difference to me is what guy I’m talking to. To most of my non monger friends, they are mistresses. They know I help them and it costs about the same as the civvies they bang, so they just call them mistresses.   To my monger friends, they’re sugar babies.  

No real difference in my mind. Just that the hotter they are and the more I like them, the more I’m willing to spoil them. The only difference is the wife, who I lie to but spoil and treat better than my sugar babies.