You really can only put demands on yourself about this. You can refuse to be at family gatherings where that person is present, but to demand your partner do the same may be too much.

I chose to set a firm boundary FOR MYSELF that I would not be in the presence of my molester. I let my family know that so they would be aware of why I might not attend certain family events, but I did not put any demands on my family to do the same. I can't set other people's boundaries for them.

In demanding your partner set a boundary, you may be setting up a situation that your partner may resent you for at some point. Can you set the boundary for yourself and allow your partner and the rest of the family to come to their own decisions in their own time? They are dealing with this in their own way themselves. It may take them longer to get to where you are because they have the additional weight of actually being related to this individual -- it does add a layer of internal conflict for them.

By the way, eventually my family got there too. They just needed time to find their way through it and to that point, but I let them get there on their own.