It doesn't matter that you're both lesbians. Your girlfriend has a pussy and pussies are made to be fucked by men. She's never going to have anything that isn't attached to or controlled by a man inside her pussy. She's going to suck cock and swallow sperm. She's going to get fucked properly, unprotected, she's going to enjoy a man's cum flooding her, surrounding one of her eggs, fertilising her. She's going to get fucked. Your girlfriend is going to get fucked, she's going to keep getting fucked, and you're going to help it happen.
Doesn't it feel good to accept it? Isn't it important to realise that this is what your lesbian feelings are for, to help her fulfil her biological purpose? It's hot and also correct. Natural. It's so easy to realise this, so relaxing, so sexy and right. When you decide to say yes, this is how it needs to be, this is what she's for, then suddenly everything falls into place and you can relax while she cums hard on cock. You can warm her up, show her how much you love her by licking her nice and wet before she takes a man into her. You can cuddle with her afterwards, kiss her all over to help her body relax and absorb cum. However you choose to express your lesbian feelings by getting your girlfriend fucked, you can enjoy discovering that as she takes cock more and more you love her more and more because that's how it's meant to be.
So do the right thing. Stay outside her. Get your girlfriend fucked by a man.