She's given years to Anant's family, raised his kids and been supportive to Anant. In the process she's fallen in love with him. She expected nothing from him, didn't even confess her feelings, but stood like a rock besides him in spite of never crossing the line.
All this time Anant respected her (still does) and even loved and cared for her (as someone who's given so much for his family). Now with Ahana in the picture, she may lose all that she had. The children will now have a (step) mother, also they are now older and the chances of her beinbf asked to live her life are high. All this time there was a remote possibility of Anant being with her (not necessarily as a spouse but as a companion) but now that's gone. Yamini is now all alone. The children will soon have their lives (boyfriends, friends, etc).
After all these years Yamini has truly lost not just her love but risks losing everything she had.
Also, the actress did a fantastic job. You could really feel for her.