What a divine question! No, I’m being serious, because so often the matter of (un)faithfulness gets reduced to a technicality.

So, a straight man who lusts after other women, flirts all the time, looks at loads of porn and inhabits sexually explicit chat rooms, but never actually has sex with other women, can say: “But I’ve never been unfaithful”.

Or a lesbian woman can deeply desire other women, or fantasise about sex with a man, and be wracked with guilt about these desires, even to the point of withdrawing from her partner.

I think we all have so much baggage about faithfulness – and a lot of this is tied up with our upbringing and even our faith. Academics disagree about whether faithfulness is the “natural” state for humans, and about gender differences.

My bottom line is that, as much as possible, we should be open with ourselves and our partners. Secrets take their toll. Some open relationships can work if both parties talk about it and desire it – for other people this can never be acceptable.

But enough of the lecture! To get to your specific question, I would say that, technically yes, it is still unfaithful if you, as a gay woman, have slept with a man.
But relationships and actions are not technical: I am interested in why you want to know and what you want to do. It seems as if, what you did is weighing on you and I would suggest you chat with a counsellor to work out what it all meant for you.