For
same sex couples, I believe the union is termed
Eingetragene Partnerschaft ( French Partenariat enregistré fédéral ) for Federally Registered Partnership. This
link gives some information though not authoritative, and probably dated. There is a
Wiki entry too.
The BFM has a PDF file
here.
Your Swiss parner might wish to reach the
Pink Cross for advice too. There is a thread
here as well with links to eg.
www.360.ch
Hope this will assist you in some small way. Good luck.