During the judgment, he calls bullshit on the "I didn't love you" claim. Inquisitor spoke without thinking in an emotionally charged situation. That leaves him in a situation of having to think really hard: did she mean that? When the judgment comes along, now he refuses to not face that, to not address it. He wants to come clean, he wants to stop living lies, and seems to want her to do the same. Calling her out in front of people wasn't likely wise given his talk of corruption and all that, but as someone acting on feeling, it worked for me. It made it feel like he wanted things to work that much that he just refused to hide it any longer. It was a very human reaction, a reaction that came from feeling and a desire to tear down the wall (har har) of lies and deceit.
At least that was my take. People's mileage may vary. It also made the kiss a little easier to take in that the situation was then elevated to a point where I felt that both Blackwall and the Inquisitor needed some assurance that they could move forward together.
Still would have preferred the kiss to be later, but my brain strung it together better when I was a bit of a jerk to him in prison. 