Since your tank is 55 gallons in volume, and if you don't want to give the lonesome male away, you could add another female for the Romeo (lol) - if your tank is not overstocked, of course. If the two pairs would fight with each other, you could use a tank divider. If you don't want a tank divider ... I'd suggest another tank for the Romeo and his new lady
It's very possible that the current pair you have would fight with Romeo and his new lady. I know that from what I have observed in my angels. When they spawn, they become aggressive. Luckily for me, they limit themselves only to chasing other fish in the tank. But it could have been far worse. Just so you know.