Pour les français, c'est très court: Louis et Gwen se sont pacsés le 2 avril. Vous n'avez certainement pas besoin d'explication. Au cas où, il y a une définition sur Wikipedia.
For the rest of you, Louis and Gwen have signed a PACS. So, what's a PACS? Well, there's a Wikipedia explanation in English. But it's a bit long. The short version is that the French passed this law in 1999 that allows couples that are not allowed to get married to have a contract that gives them all the same benefits as married couples. It was designed for homosexual couples. Since then, heterosexual couples have adopted it, too. Instead of going to city hall for the civil ceremony, they go to court for this contract. And if they decide to split up, it's back to court. It's easier to terminate this contract than it is for a married couple to get a divorce and I think that couples today are not as optimistic as before and they are concerned about the end before they even get to the beginning. That's what makes it more popular.
For a parent, it's certainly less expensive than putting on a wedding. Like when a couple elopes, I guess.
Anyway, they did this now because they are about to buy an apartment together. Paul has visited the apartment but I haven't seen it, yet. From all reports, it's very pleasant and not far from where Louis lives, already. It's much closer to the metro station and shopping, still in the 14th arrondissement.