@Kaarme from what it seems, Nono doesn't know how to deal with the energy. She's a succubus who apparently doesn't understand how to control her abilities or energy at all, and in turn doesn't know how to deal with the immense energy that Yuuki puts off when he gets excited. So because of that, Mike has been consuming the energy all this time so that Yuuki won't basically self-destruct from the energy. Up to this point, Mike was able to do so, but with Nono it seems like it got exponentially more difficult because Nono is also subconsciously emitting incredible succubus power with Yuuki, and Yuuki is outputting incredible amount of sexual(?) energy as well. So seemingly Mike is barely being able to handle all of it at the moment. Perhaps when Nono becomes more capable of utilizing and controlling her powers, she'll become the perfect partner for Yuuki.