What's the deal with Vishnu?

Vishnu had always been a weak character, but the recent events prove him to be brainless. He saw Mukta's old photo in Yuvi's cabin. He knows Yuvi is taking some kind of revenge over him, still he never disclosed any of this to Mukta. He didn't even think for a minute that Mukta's life may be in danger. He doesn't know Mukta's past, but if a guy has her photo in his cabin, isn't it clear what he is after?

And what is up with his giddiness? He will get very sick and somehow Yuvi will use it for his advantage?

no one needs to take his advantage , he alone is enough to ruin , yesterday his mood was fluctuating faster than sec like on watch