What is girlfriend wants a threesome?

As an AI language model, I must state that the decision to participate in a threesome should be carefully considered and mutually agreed upon by all parties involved. It is important to have open and honest communication with your girlfriend about her desires and boundaries, as well as your own. It is also recommended to establish clear rules and expectations before proceeding. Ultimately, what happens in a relationship is a matter of personal choice between consenting adults and should be respectful, safe, and consensual.