Guru is not antagonist. He is the true well wisher of Mohan. I dont agree with those who think he should be slapped.
He understands Mohan pain and he was the one with him all through 12 years of pain which Guru only has seen and no one else. Guru is wise to tell about Rimjim as Mohan and Meera daughter just keep Megha away from Mohan. He understands it so well that inspite of so much of love she misunderstood Mohan for Addu, She will never understand his true love for Megha or her family.
If i keep myself in Guru place for a sec, i honestly would have done same thing which Guru did today. I know its not correct, but there are hell lot of things as well which are not correct on the other side.
Guru did what he could do to save Mohan. And though i want and honestly like to see MM together as a happy family again, for now, i want Megha to go through the feeling of jealousy/ redemption phase now to realize what she did actually to lifes of their most loved once, Nanhi, and Mohan.