took her to that spot
just to break up with her. I don't think that had been his initial intent at all. To me, it felt like after he had kissed her he sort of...had a realization? He realized things couldn't continue as they were. We don't know why or what brought him to that conclusion at that exact moment. Perhaps he had intended on doing something more, perhaps he looked at her and realized he was about to push the envelope even further and reigned his emotions in. Maybe he saw her and realized he really just wanted to throw it all away to be with her and he had to remind himself(through her) about distracting one from their duties.
He could have seriously been debating on staying with her all this time, we don't know one way or the other. And if so, we don't know what made him feel like that wasn't an option any longer. The mark? The fact that Cory almost destroying the world is pretty much a direct result of his actions (although he would have undoubtedly found another way)?
It really just feels like we don't have enough information to determine what his initial intentions were beyond what he told our Lavellans when he took them to that spot, which was to tell them to truth and express to them how much they meant to him. And I think that's the point, we're not supposed to know why Solas broke up with Lavellan, but I don't think he took her there for the sole purpose of breaking up. I think one option Lavellen is like "You're my..." and he goes "That is the question, is it not?" Maybe he had intended to answer it, and after that kiss realized he couldn't, at least not the way he would have liked.
I don't know, I just feel like his behavior at the end is too inconsistent with everything before that for it to have been planned. Apologies if I seem fussy, I've just seen this accusation come up often and after a lot of thought I just wanted to throw my two cents in.