My mother in law

I am a happily married man with children . My wife's mother for the passed 14-15yrs looks at me in a way that has me curious to what the look is all about . She tells me things occasionally along the lines of her sex life isn't all that , I'm her favourite son in law (even though not her only son in law), compliments me a lot and squeezes me tight when we hug during greetings when we make plans with them. I know it's crazy and can only imagine the tremors it would send through the family if it were to happen and someone found out. This curiosity on the other hand I wish I knew how to tell her how I feel and what we hopefully both want .I master bate with her in mind 100% of the time that I do . I know she loves sex but her husband has a tough time getting it up and tries Viagra .But according to her comments to me that she isn't quite satisfied. I never had sexual feelings for her before but they just keep getting stronger and stronger to a point I want to ask her if she would secretly like to have sex, I just don't know how as she is my mother in law . Is this normal?