Is there any hope in waiting for someone to be single again?

I’m afraid I have fallen hard for a close friend who is currently in a relationship. We met when we were both involved with other people and I consider us close friends, so I don’t think she ever considered me as a potential partner. I have no desire to try ruining her relationship, I just can’t help waiting around for her. She has never shown any obvious romantic interest towards me necessarily but I’m so delusional that I believe this is only because she’s been in a relationship, that she is going to consider me once she actually starts looking around. I know this won’t happen, that it doesn’t work like that. I am trying to convince myself I can no longer think healthily so I can try pulling myself out of this obsession. help me by saying that there is no hope.