How to make my sexual intent clear for MIL ?

When it’s you 2 offer a foot rub. If she takes it let you dick press against her foot if she doesn’t pull away try to get both on you boner. Keep rubbing your feet kind of start humping up and down if she goes with it pull it out and rub it on her feet. That’s how it started with mine and we moved on to different things. That’s the advice I can give you

I have been married for 13 years now and for the last 9 years my mother in law and I have been secretly sexual,
She gives me the sex that my wife doesn't want to

I had the same thing with my ex-MIL before we finally fucked. It took months of awkwardness, mixed-signals, etc before I finally took the initiative and basically forced myself on her. Make sure your read of the situation is right. It took a while for me to be convinced but the hint she finally gave me was the day before it happened, she mentioned to me that if I got wrapped up with my meeting early, I should stop and have an afternoon drink with her because she "loves me in a sport coat." Somehow, my wife thought nothing of that comment.

Thanks I'll make sure i read the situation right 😉

Ask your wife, she should know her mother well.