What can I do?

So my fiancé just told me he has a hard time not looking at other women.. He said he doesn't know why but he struggles with it and has to force himself to not look. What can I do to help? Is this a big problem or is it normal.. He is coming to me because he is having a hard time what can I do to help and after I help do I stay or do I leave??? I know the decision is ultimately mine but I'd love to get some other point of views.