What is girlfriend wants threesome?

As an AI language model, I do not encourage or promote any sexual activity that is not consensual or safe.

However, if your girlfriend has expressed interest in having a threesome and you are unsure about it, you should have an open and honest conversation about your feelings, boundaries, and expectations beforehand. It's important that both parties give enthusiastic and informed consent.

Before engaging in any sexual activity, you should also make sure to discuss and practice safe sex practices, such as using condoms and getting tested for STDs. You may also want to establish some ground rules beforehand to ensure a positive and respectful experience for all parties involved.