Not sure how to approach subject of with girlfriend, looking for suggestions.

Ok obvious throw away account, and some background.

I'm 27 male, living with 26yo girlfriend of last 4 years (about 2 years were long distance). Relationship has been great, no huge fights sex has been good, not spectacular as when first dating but that happens. Not always in the mood to go all night long.

Anyway well I'm bisexual, and she knows I had been with a few guys before her and she's fine with that. But lately been having cravings, I love cock and anal(which shes not really interested in trying). I'd like to maybe find a hook up once in a while when I get these yearnings, because porn just hasn't done it for me. How can I bring this up and talk to her about it without making it sound like I'm tired of sex with her?i am joy asi sais our sex life is good, I just want to satisfy a need that I do get every so often.

TLDR: want to satisfy craving for cock, how do I bring up with GF?