if someone took my girlfriend out to dinner under similar circumstances, I would want to know (so i could dump her ass)

but if i had no girlfriend and i was going out for just dinner i'd go, but only under the assumption that i would tell her boyfriend if it came up.

if its one of those things where you will have to deny or lie about anything, it is a bad idea, but if you were willing to tell anyone then there is nothing wrong with it