Getting a divorce in Michigan

We knew each other for 5+ years & started dating right away, we got married this past August, so it's been about 5 months.

He has "cheated" before, I put that in quotation marks because I don't know if he actually ever slept with someone else, but has been on dating sites, tinder, I've seen emails with his dick pic attached & I consider all of that cheating.

I was dumb enough to marry him knowing all of this. Why? Because he told me he would change, he promised me on our children's lives that he would never do it again & I was naive enough to believe him.

Today he was taking awhile to get home from work, so I decided to make a fake profile on one of the dating/hook up apps he's used before & long & behold, there he is. His picture. A picture he took on his way to his bachelor party. A week before we got married. I believed him when he told me he loved me & my heart completely shattered.

I screen shot the profile & texted him, he says that's not him & what am I talking about? Then it takes him another 3 hours to get home. I told him I wanted a divorce, he said no. So my question is, how can I go about this, without him agreeing to sign anything? Can I still get a divorce, or am I stuck in this marriage with a cheating pos?

Sorry this is so long, I really don't have anyone else to talk about it with, since everyone had their doubts about our marriage too & I'm sick of looking stupid because of him