(bbm)
I think you nailed it right here. I would hazard a guess RA's attachment to K is much more about what she symbolizes than anything to do with her as a person or how desirable or not desirable she is to him. With her, he's a married man, a father, a provider, whatever. She is a key part in maintaining his illusion of being a normal, successful, well-adjusted and functioning man in society and without her it is much more difficult for him to fend off the deep feelings of inferiority and fear of people thinking poorly of him, things that have seemingly plagued him for a very, very long time if not his entire life.
We know he certainly wasn't thriving in the working world. He doesn't seem to have been particularly well-liked or had a lot of friends. What else is left to measure any success (and again, normalcy) in his life other than his marriage? I think the fact that he professes to care so much about her but repeatedly ignores how she is feeling, even when she's expressly asking him to do/not to do something (i.e. in the interrogation w/ Holeman and prison calls) supports this. It's all about him, and how he needs her to make him feel.
Eta I recall Holeman noting in the interrogation, when they were just chatting before things got serious, that RA seemed particularly proud of the fact that he owned his home. Another thing crossed off on RA's list of "how to be normal" imo
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