Wil,
I just wanted to say that
"I expected one of us to eventually be pushing the other in a wheel chair at some point in time, growing old with each others wrinkles..."
is a great visualization of what many of us are looking for (and cannot find).
You said,
"...it was I who chose not to fulfill her needs in the relationship, which caused her to look elsewhere."
--> I think you have beautifully summarized what causes a lot of relationships to fall apart. Some people are fully justified in choosing not to fulfill their partner's needs, while other people are not justified in doing so at all. But either way, the result is the same.