Girlfriend moving out

General Discussion

Boyfriend and Girlfriend (Joint 6 month AST) have been renting a property from me since April 2019. The girlfriend has informed me in writing that she is moving out but her boyfriend wants to remain in the property. Do I need to issue a new AST to him or can I add an amendment to the one he has?
How soon would I need to do this because this happened last year when they had a fall out but they were back together within a few weeks?
They are both excellent tenants who look after the property and have never missed a rental payment.