I don't think that is definitive. It still is not clear who initiated sex in the back yard. In my mind, "you could have always said no", is simply shukandjive from Boss. Implied consequences were always there. Levels, layers. And if what Boss says were actually true, there would have been no reason for her to say in the final scene.
But rember...
or for him to reply
I know-I know...Husband...noble sacrifice...I get it.
No reason to say that at all. There would have been mutual understanding of the situation, but that understanding was still lacking. Mostly because of Boss's shuckandjive.
For me this final scene is them beginning to be honest with each other about the situation and what is happening between them. Everybody needs to get a lot more honest in this story. Because long term relationships cannot survive otherwise. A breakthrough of honesty for Wife and Boss is significant. A similar breaktrough for Wife and Husband could again cloud the situation, depending on what is said. Not that I am cheering for Wife and Boss. I would say the conditions for a successful relationship for them would be the same as for anybody. Unless SC wants to bless us with more fantasy around that.
So for a final linking of the lives of Wife and Boss three things are needed
1) Husband needs to go away one way or the other
2) Boss needs to get a lot smarter about satisfying Wife's emotional needs, with his understanding that is not the same thing as sexual needs.
3) Wife and boss need a serious conversation where they really do say the words, not in the middle of sex, and commit to each other mutually. If he owns her, she needs to know that she owns him. Otherwise, in the end, no deal. Not immediately, probably, but over a period of a few years a spouse starts realizing the kind of jerk they are hooked up with, or not. If not, happy satisfaction can ensue and years roll by.