The OP was talking about "model or female celebrities" and since this is a purely hypothetical scenario I am going to join in. If this were her:
Then yes, I'd prolly cheat. Sorry, I'm shallow like that. I mean come on. Are you going to tell me that you ladies if faced with a famous movie star of your picking WOULDN'T cheat, or at least be sorely tempted, I mean please, this is a hypothetical exorcize were talking about here. If Brad Pitt came up and said he had to have you, you would say:
“Nope, I'm in a committed relationship and I wouldn't do that to my partner!”
I'm just not not buying it.
Guys, look at her, I mean look at her real hard, and say that if she threw herself at you, as the OP suggested, as preposterous as that is, you would turn her down, committed or not.