Alex’s reaction to Piper saying ‘Why do you always feel so inevitable to me?’ makes me feel so, fucking, much.

inevitable (ɪnˈɛvɪtəb(ə)l/)adjective - certain to happen; unavoidable.
noun - a situation that is unavoidable.

We know they’ve both said i love you-s before, but I think that this line means even more to Alex than an i love you. By saying Alex is inevitable to her, Piper basically says that she can’t live without Alex. By saying always in the same sentence, she’s saying she can't ever live without Alex. Ever. It takes Alex by surprise, like we all can see, and she doesn’t know what to say back. She also realises a 'simple’ i love you wouldn’t fit so she comes back with i heart you, which means the same but in a way she makes it more exclusive: something she would only say to Piper. She may be saying i love you to more people, like her family or friends, but i heart you is only for Piper. Because she feels inevitable to Alex, too. She always does and she always will.