Hi,
It actually sounds like your “male” is a female. You may have two females, or the other bird may be a male if it has never laid eggs. The females are the ones who get possessive over the nest box or cage and will attack if you get too close. Because this bird took over the nest box, and isn’t interested in the other bird, I think you have two females. The best thing to do is remove the nest box. If you have two females they do not need a nest box. A nest box is only for breeding pairs and should never be left on the cage all the time. They do not need a nest or bed to sleep in. A nest box should be removed in between clutches and the pair rested for 6 months. But if these are both females, you need to discourage more egg laying, which means take down the box and do not ever give it back to them, or give them anything else they can nest or sleep in. You may have to split them up because the female lovebirds are very territorial and once they start acting this way, they usually will not allow another female to be in the same cage. The only way to tell if lovebirds are male or female is with a blood test – no matter what anyone else may have told you. Or if a bird lays eggs it is of course female. Even if this is a male and female, they are clearly not bonded as a pair so they will not be good for breeding.
Thank you for asking Lafeber,
Brenda