Even with Don's massive infidelity, I don't think Betty would have told Don she didn't love him had she not connected with another man (Henry).
The question is will Betty be happy in defining herself by her man and without personal growth. In her defense, Betty has demands with her kids and maybe not a ton of time for personal growth, except maybe as a mother. Yet, Betty's mom apparently did a good job conditioning Betty who seems to still live in the 1950s.
Compare Betty's lack of personal growth and being content(?) in the olden days (and being the beauty for her man) with Peggy's personal/professional growth and breaking barriers. Though the Peggy/Duck thing seems off to me. More power to Peggy I guess.
I was 4 months old when JFK was assassinated.