this is a hugely sticky situation, and i don't envy you being in it. you were trying to do a good deed and look what happened?

so let's look at both sides.

IF YOU TELL . . . the way i would handle this very situation (and i have been faced w/a similar one. .. ) i would talk to your brothers gf. in private. meet her for lunch or a coffee, and explain that you weren't ''searching'' but it was impossible to avoid. and that you know she owes YOU no explanation, but you feel like you have to talk to your brother about it. and you wanted to give her a heads up, and the chance to talk to him about it FIRST.

this may affect her feelings toward you, in a negative way, and possibly forever. but it could affect your relationship w/your brother if he finds out you knew and kept it from him.

NOT TELLING. . .. it is her private computer and email. sometimes things can be taken out of context. and. . . i am in an exclusive relationship, but i have ''flirted'' in harmless ways, with other guys. (would never date them, or even meet them in real life unless i told my bf, and only if he approved) however, i have not ever been to a 'dating site'. still, it could be innocent and harmless flirting, no plans to ever meet , etc.

if she went to those sites during a down-time in their relationship, then who's to say he didn't also do the same? or maybe he already knows she dabbled in dating a bit during that time.

but will this bother your conscious, if you keep it inside?

BOTTOM LINE - there is no perfect answer. it's a prickly path either way you go. ((me? i would choose to tell her. and let her know i am definitely talking to my brother in 3 days.))

good luck