Gargh! It makes me all stabby on your behalf! What disgraceful behaviour your mother-in-law has displayed. How dare she? Seriously, what makes her think she can betray her son's trust in that way? Let alone yours??
Steph, I am SO sorry this has happened to you. You have no control over this disease, the least you can expect is to control the dissemination of the information. All I can say is take some deep breaths and try to let it go. But note to self, when people show you who they are, believe them. Your mother-in-law has shown she can't be trusted. In the future, don't. K xox