My husband knows I check out this site. And he doesn't mind. He was the one that told me about LPSG and helped me sign up.
I think being open and honest with someone that is important to you is a good thing.
Doing things behind people's back's usually blow up in your face when you least expect it too...... and it can bite you in the butt.
I think most guys probably don't mind having a girlfriend that likes to look at guys with big cocks. They probably understand and are flattered that you are with them. Everything should be fine as long as you are able to let them know that you like whatever equipment that they have too.