"It's not you; it's me." Class break-up line right? Maybe even cringe-worthy.
We tend to think of it as an excuse when people don't know what else to say, but maybe that's a bit harsh because it's often true. It doesn't mean there's anything wrong with either of you; you're just not necessarily right for each other.
What about this one? "If I'd just met you sooner…" or "I'd totally marry you in ten years". Yeah, it doesn't feel any better, but think house hunting. Maybe this particularly house would be great in five years, but it doesn't work for you today because of some circumstance--proximity to a school or an infant that needs a room close to a master bedroom. Ultimately people's needs change.
That brings me to Query Lesson #3. Whether we're searching for a house, a job, a friend, love, or an agent, sometimes, two things drive the match: "fit" and "timing."