The source would be all the interviews he's done discussing it, clearly agitated, the fact that he has dropped out as director, his film history (non directorial) which has been less then stellar, the critical reception to BvS, the entire link that I posted regarding his rumor of wanting to leave all together, and the list goes on.

I don't think one says:

"“It's one of those things that's really frustrating because with Live by Night, it took me a year and a half to write it and get it ready, and I worked really hard, and nobody gave a shit,” Affleck said. “Nobody was like, ‘Where’s Live By Night?!’ But with Batman I keep on getting, ‘Where’s the fucking Batman?!’ And I’m like, ‘Whoa, I’m working! Give me a second.’

or

“Oh my God, it’s such a pain in the ass. It’s like every time I mention Batman it gets this huge clickbait,” Affleck said. “When I was doing this movie it took me two years to get it together, but nobody ever asked me, ‘Where’s Live By Night?’ You know? They ask me ‘Batman, Batman, Batman.’ Batman’s coming along, it’s going to be great. We’re going to make something really special. We’re going to take the time to make it right. We’re going to do it good.”

Then drops out of directing it because they are happy with what's going on, and not tired. And sorry, but that's the extent of the source I will give, as there's a reason this is a link to begin with. Anything else you want to know, you can use google for, it's not difficult. You can believe me, agree/disagree, or not, but I'm not here to do anyone's work for them because their to lazy to look into it themselves.