You need to separate them immediately or he is going to end up killing her. Birds have to be introduced to each other very gradually. Especially lovebirds and particularly one who already had a mate. If the new one is a lot younger than the male, she should not be put in the same cage with him until she is about 2 years old. It’s dangerous to put a young female in with a mature male. He will end up wanting to mate with her and she will be too young to know what he wants. He will then end up attacking and killing her. He has no use for an immature bird. She will start maturing between 8 months to a year old, but she still should not be caged with a male because she shouldn’t start laying eggs until she is 2 years old. If you let a female breed and lay eggs when she is too young, she is at a high risk of becoming egg bound and dying, and she is also too immature to care for eggs and chicks properly. She can develop bad breeding habits that will ruin her for being a good breeder later on. Even if your plan wasn’t to breed them, being with an older male is not safe for her. You can let them be in cages side by side, but do not cage them together until she is old enough.
Thank you for asking Lafeber,