That is the wrong interpretation of fulfilled though. Jesus had a way more stricter standard/interpretation of the law then what was even in the OT (Old Testament, or what you would provide a context to what you call "Law and the Prophets").
The OT allowed divorce. Jesus forbids divorce and remarriage and calls it adultery.
The OT says not to commit adultery. Jesus says if you look at woman lustfully you have committed adultery in your heart.
The list goes on and on.
Just because something is okay in the OT (I.e multiple wives and concubines) doesn't mean it carries into the NT or is endorsed by Jesus.
Anything that sounds like it's "Okay" in the OT may be "okay" because its a compromise from God's standards in order to keep things functional with the ancient Israel society rather than being the original intended purpose in the first place. An example of this is the OT allowing divorces. God did not create divorce in the Garden of Eden with Adam and Eve, and Jesus endorses that first intent.
Based on the standards set by Jesus and the Apostles, I can tell you that multiple wives and concubines are not endorsed anywhere and might even be seen as a type of adultery or fornication. Unless someone is already in that set-up once they come to faith then that's one thing they have to sort out, however after someone has come to faith, they wouldn't be interested in woman out of lust like that in the first place.
A better understanding of fulfil is applying love to the equation. The command not to commit adultery is fulfilled by loving your wife. If you love you wife then you will not want to commit adultery against her. In the flesh, you can't really love you wife, because the flesh only understands lust, not love. If the grace of God touches someone's heart and they love their wife then they are not only not committing adultery against her, which is honoring that command, but are fulfilling the law by also loving her. It's possible to not commit adultery and hate your wife and cuss and fight every single day, but that would be failing to fulfill the law despite you are not breaking it by committing adultery.
In terms of wisdom, the proverbs never encourage adultery of any form but instead it encourages solitude compared to that situation. It didn't say "it's better to have multiple-wives and concubines, or visit prostitutes than deal with a quarrelsome and nagging wife", did it? It said, it's better to live alone and in more modest circumstances than to live in a mansion with a bad wife. That would be a more fitting interpretation.