Welcome back to the forums,
Yes, unfortunately your Bijou is showing clear signs of aggressiveness and in order to prevent the situation from escalating further, for Louis' overall mental and physical welfare, it's best that he is housed in a separate cage.
And this is to be followed even after the quarantine is ended (even though it was broken in the process by introducing the newbie too soon).
Why do you have a nest on your budgie's cage? By keeping a nesting area, you are triggering potential breeding behaviour leading to egg laying.
Your female can certainly get broody and the current aggressiveness exhibited can also be even further potentiated and fuelled by the presence of the nest in the cage.
Both of your budgies are way too young (especially your male) to breed and given Bijou's aggressiveness this makes her not a good candidate for future breeding, because this aggressiveness can have disastrous consequences on a potential future breeding journey, where the chicks would run higher risks of suffering abuse, not to mention that they could also inherit the less than desirable temperament from the mother.
Please remove the nest from the cage and follow the recommendations on this link: When We Don't Want Eggs!
It's imperative that your budgies are housed on separate cages from now on. Much later on you can allow them to have closely supervised out of cage time together and depending on how they behave you can continue the arrangement or not. Still, it's best to keep them on separate cages on a permanent basis.