(remember, massive spoilers, I'm just trying to record my rambles here. I may make mistakes, this is all as best as I remember it)
So, Act 1 ends with a bang (to Evie's great dismay, she got Flissa out but was too slow to save Minaeve. Like, was literally standing on the fire trying to disarm it when it blew up, leaving a charred corpse, which was kind of traumatic, and she was my favorite of the Havensfolk too. Saved Threnn at least. But I was way too caught up to savescum so what happened happened.) Lots of big emotional scenes, dramatic stands, charging out to defy the Big Bad, potential heroic sacrifice to save the others... although I don't think Evie really thought she would die. She was kind of too angry to be scared, and as the player of course I knew the game wasn't over yet. And then the big stirring scene and the plans for the future.
By this point, Evie was absolutely ready to lead the Inquisition... not for religion, but to do what was right. It was her duty, and no one else could do it better. If people were going to make her a creature of myth and legend, she was going to use it. Maybe she was chosen, after all. (She'd lived through that craziness and come out with superpowers, hadn't she?) Maybe she really was the Herald. Maybe she would be Empress. There was no more reason to deny her destiny.
So emotionally, Evie was riding a high.
On a meta-level, I'd stopped thinking of all the heart options as necessarily flirtatious, since many of them just seemed NICE (After all, I was hearting on Cassandra all the time and it wasn't really being more than friendly) so when the option popped up to tell Cullen I was glad we'd both made it out of Haven alive, of course I picked it. I was glad we were both alive!
And then his voice drops, and with this painful intensity Cullen swears to protect Evie from anything like that ever happening again.
In her heart, right then, something went ping.
But it was silly, of course. He was just some boring old ex-Templar and she was pursuing an elf girl, when she wasn't flirting madly with Dorian or palling around with Cassandra. They parted ways. Meta-level, I didn't even figure out where Cullen's position on the Skyhold map was for a good while and couldn't visit him if I'd wanted to.
Evie went back to hanging out with her friends. Met up with the Bull and his Chargers. Started getting to know Varric a little better, and mediating between him and Cassandra. Preparing to find Hawke and the Wardens.
(Oh yeah Blackwall happened at some point but Evie found him a little unnerving, she mostly only hung out with him to try and find out info about the Wardens.)
At some point, still chatting up Sera, I got the pranks quest, and Evie set out to have a little fun... only to be dragged into Cullen's office and told to play a joke on him.
She couldn't do it. Josephine, sure, but Cullen? She could not bring herself to diminish or discomfort that man in any way, not even for a moment, not even for Sera. It was unthinkable.
And that's when she knew she was in love.
(Meta level, from checking the wiki it looks like this may actually be the last step with Sera before you start a romance properly. I honestly didn't know, because it pretty much happened just like this - after that point i went for Cullen with no hesitation, and never even had a conversation with a flirt option in it that I can remember until after Evie and Cullen were a couple. That kiss just about killed me.)