Anal Only Lifestyle Forum

We're a MF couple with myself a Bisexual Hetero Romantic (Sexually attracted to both sex but only opposite sex for relationship) and my gf is a Bisexual.
We have discussed my interest in being pegged and she's happy to try it out, but she doesn't know that I have been doing anal masturbation for a few years and able to fist myself or take big toys.
I know truthfulness / trust is important for a relationship but I'm anxious that she may freak out as she doesn't do anal herself and more on the vanilla side to sex.

And so I was wondering if I should keep it all a secret and start small, so that we can both enjoy training my hole.

What shall I do??

Even though it might seem scary at first, opening up is usually the way to go in these situations, at least in my opinion. I get a sense that you might be afraid of being judged by her or even losing her? Tell her about how you feel and gradually open up. Withholding something because it's private and intimate is not the same thing as telling a lie, and opening up about intimate things usually builds trust.
And btw anal masturbation is very common for both genders.