I had been thinking, "What does Ian do TO strengthen our relationship", but the problem with that was that "TO" indicated, to me, doing something "for the purpose of", and I don't think he does anything "for the purpose of" strengthening our relationship.
But then I switched to thinking "What does Ian do THAT strengthens our relationship". To me, "THAT" indicates less "on purpose" and more "just happens", so I was able to honestly write
Ian strengthens our mother-son relationship when he speaks to me in a courteous, respectful way, fulfills his responsibilities without being asked, and sees something that needs to be done and does it without being asked.Phew! Mission accomplished
(Also, Husband is home and shouldn't have any weeks-long trips coming up!!)