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 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.