A lot of people are saying it would be a huge betrayal to Eleven, but Mike is a horrible boyfriend. Mike does not love Eleven. Maybe a little but not enough to say he's a good boyfriend. I have a theory
Mike will go to Will and talk about the tension. Mike will tell him that he has a girlfriend and they are just friends. Mike will become curious and kind of bring the tension up a level by flirting obviously. Will will realize what he has done. Will loves Mike but thinks of how hurt El would be. He tells Mike he wished this could happen but it can't. Mike and Will go back to being friends.
Did I do good?