Yes, I am mad there wasn’t a kiss, but it makes sense in a way to me. What Stiles said- the precious memories he shared with Lydia- was far more important. He was about to be erased, and he wanted Lydia to remember him with memories they shared that he found important-the first things that came to mind when he realized what it meant for him not to exist anymore. Lydia being the first girl he danced with, him having a crush on her all of highschool, Lydia saving his life, Stiles saying he loves her- these are what Stiles wants Lydia to remember. He wants her to remember her impact on him and place in his heart, not his kiss. When he thinks about what it means to be erased- gone from the lives of the people he cares about the most- Stiles doesn’t think that something physical like a kiss is what should stay. He wants his love for Lydia to be permanent. When he is gone and no one remembers him, Lydia will feel Stiles’ love, and he will come back.