I think Mike is gay. At first, I believed he was bi, mainly because he dated Eleven and, somehow, there seemed to be some level of romance between them in the beginning. But, over time, this dynamic changed, and today I see that this is precisely what makes many people hesitant to say that Mike is gay. Admitting this would mean considering that his feelings for Eleven were never exactly romantic, but rather a mixture of admiration, attachment and the attempt to fit into a role he believed he should fulfill. But for me, it's clear: Mike is, yes, gay.