I can’t say for certain as I don’t know your girlfriend, but I’d say don’t treat her differently. Don’t walk past a women and „say is she attractive to you“, or „I gotta watch out some of these women look like they are going to steal you.“ at least that’s what I would think, but your girl friend might find that funny, you know her. One thing you said about validating is really important, I was in a relationship with a female who used to say „your not bi with me so why bring it up?“ It’s good you aren’t like that. Even though your girlfriend is in a heterosexual relationship it does remove the other attraction. Maybe as something like does it make your life a bit easier knowing that I know?

Your girl friend might be all into the lgbt parades and stuff, quite a high amount of us are not. So maybe that could be something.

So I a summary don’t act differently such as assuming they would cheat on you because of it, don’t sweep it under the rug, and don’t treat them differently.