While I'm at it both Colin and Pen are so brave and trusting of each other this season and it's a huge reason why the pacing works for me. This post from @dollypopup goes into detail about the kiss and the bravery it took for Penelope to ask and how important and meaningful it is for her ark (in a far better way than I can), but I think it can translate thought out a lot of what they both do. (Elaborating on this post.)

So much of their relationship is driven by an active want to continue, grow and improve it. They start talking again because Colin notices she's upset and makes the effort to follow her and see what's wrong, they make up after last season because, once again Colin makes the active choice to visit her, apologise, and agree to help her with what she wants. Because there is a baseline there, there is trust and friendship and respect already established from years of knowing each other and the last two seasons. He already values her and cares for her and so makes an effort to maintain their relationship. She trusts him and loves him and knows him well enough to see past this new act, and she accepts his help and apology readily.

Then their lessons happen because they make the effort the seek each other out, Colin actually listens to her about her insecurity and comfort and ranges for them to practise at the Bridgerton house because it was a safe, calm, stress free environment. And it worked, she opened up (as much as she ever dose lol) because he knows her already and she is comfortable enough around him to let her guard down and even let some of her true feelings out, even if unintentionally.

The kiss has already been discussed and said much better than I ever could lol, but it really really is so important. It's not chance or coincidence or force that kickstarts their relationship it's Pen. At one of her lowest moments It's Pen and her choice and her love and her trust and bravery in that moment to ask Colin what she wants and be open and vulnerable in a way she almost never allows herself to be, in a way woman as a whole are punished and looked down on and seen as lesser for doing (clearly, as seen by peoples reactions.) And she is reworded for her bravery by a beautiful, tender, blissful kiss. She wanted to be loved even for a moment and she so aching obviously was.

Then after that they take a break from each other for a little at least in the sense of spending time together, but they continue thinking about each other they entire time.

And in the end, even if it took some help from Violet, it's Colin's actions that lead to that ending. It's hope and bravery and love and desperation that led him storming into that ball half way through and interrupting dances and chasing carriages. It's bravery and vulnerability and trust in Pen, who has always been there for him, always been constant, always been patient and kind and steady, as well as love, that leads to him being able to give a confession like that and her feeling everything in equal parts for him that allows her to actually confess her feeling for him for the first time in the entire show.

Obviously all stories are driven by characters making choices, and outside influence definitely played a role in theirs, but so much of it was them both trusting each other and being brave enough to take a leap of faith and hope to be caught, and they always are. We (I) joke that they're stupid in love and down bad and absolutely unhinged feel loser behaviour abounds, because it's funny and true. But at the heart of it is so much care and unsaid words and bravery that in the end proves worth it because of who they are to each other and how much love is there.