You are the only one who knows,

How to steady the beating of my heart,

Nothing could ever be better than this,

It is so much more than I could ever admit,

The veracity in these emotions that we share,

It is so rare to find someone who comprehends,

How things can get too hard to handle,

The power you have deep within,

To soothe my every concern,

Brushing away every drop,

That I can clearly see that hurts you so much,

Because you would do anything to take the pain away,

Even though you don't realise all that you already do for me...

©️fallencalliope

Please remember that Deaton is the first one to say that Lydia and Stiles have a strong connection/emotional tether. That’s why Scott told her (to Lydia) that too and Malia agreed too. And I personally think that when Lydia kiss Stiles in 3x09 it’s when it all changed, she starts to see Stiles from a different view and the feeling for him starts there. 

And I sincerely believe the rift didn’t open just because of Lydia. It open because of his best friend/brother Scott, Malia and, of course, Lydia. We can’t deny that Malia and Scott weren’t important in his life! That boy is like family to him and that girl is his first girlfriend (and he had sex with her for his first time). So that’s why I think the rift start opening with all of their memories but because of the strong connection Stiles have with Lydia (and for the purpose of the show/rating/fans) it opens.