How do I tell my partner?

So, I lost a two year streak and I don't know how to break it gently to my partner. It's not the first time this has happened but I believe she may be more devasted than she has been in the past as it's been so long. I hate to see her cry during these moments, but I know I have to be honest with her. I'd appreciate any advice or encouragement so I can get it off my chest sooner rather than later.