Always described as “laid back” and an “eternal optimist” by those who knew him, he was now quick to anger, especially when his things weren’t where he expected them to be. A once successful and busy urban planner, he could no longer do professional work, nor could he keep pace with carpenters or handymen, jobs he had excelled at previously.

Before his accident, he was often the life of the party, cajoling friends into dance competitions. He designed an obstacle course for my birthday, made a glow-in-the-dark hula hoop to use at our annual big group camping trips and organized 10 grown men to dance to Beyoncé’s “Single Ladies” for my bachelorette party. Now he tired easily in social situations and would nap in a quiet room or sit with his eyes closed in the corner.

Our marriage suffered, mostly because our once shared burdens of work and home now fell so much more on me. But there were also surprising upsides. Early in our relationship, Christian had resisted getting a dog, even though I wanted one, because of how it would tie us down and hamper our travel. Neither of us wanted children and he’d happily gotten a vasectomy. Now he expressed a desire for both dogs and children, and talked about reversing his vasectomy, making me second guess my decisions.

Eventually we were able to resume our long bike rides, with him on a recumbent tricycle (lacking the balance for a two-wheeler). He used to ride in front, acting as my wind block, guide and protector. Now he trails behind. I look down at his helmet, at the person on the bright yellow recumbent tricycle and wonder, “Who is this stranger?”

His sense of humor has remained more or less intact, if differently delivered. For the first Halloween after his crash, he dressed up as a person with a head injury, wrapping his head in gauze upon which he’d dribbled red food coloring. Around his neck he wore a sign that read: “Too soon?”

Yes, too soon, his friends said. (But it was funny.)

What does it mean to grieve someone who is alive, but who walks, talks, thinks, acts and looks different from before? The experts call this kind of loss “ambiguous grief” or “unconventional grief.” People with loved ones who fall prey to Alzheimer’s may experience this, as may parents whose children become alcoholics or drug addicts.