You are a dual UK us citizen female living in the us planning to return to the UK can your boyfriend lived with for 5 years a us citizen and you file for a civil partership so he can stay?

Yes, as a dual UK-US citizen, you can file for a civil partnership with your boyfriend, who is a US citizen, while living in the UK. This would allow you both to establish a legal partnership, and he could potentially apply for a visa to remain in the UK based on that partnership. However, it's important to check the specific visa requirements and application processes, as they may vary. Consulting with an Immigration lawyer could provide tailored guidance for your situation.