pretty sure he's cheating....

He says he loves me. He says he wants to marry me. But lately he fights with me majorly about petty things. 
Tonight. On New Years. I told him to please not be grumpy tomorrow with me and the kids if he is to be hungover. 
He took that as I told him he couldn't drink, and has been mad at me since. 
So now he's sleeping on the couch. 
I looked through his messages. More glanced at it then actually looked and found a message from his ex. I'm screenshoting it into this message. 
He's normally always home. Except this one night where he went out drinking, called her four times, then disappeared for the night. He says he ended up at his moms house and that his ex apparently had to carry him up there. 
I never saw the message from her. 
This is the message she sent him just the other day. 
My heart is breaking. I do everything for this man. I feel like the ultimate failure, for my life and my children's lives. 
Please tell me how you would interpret all of this. 
We have been together a little over a year and never had any suspicion he was cheating on me until after the night he came home from staying "at his moms house"