I'd say the day you said '"fuck it " and set out to find someone else was the day she was being moved out of the primary position whether you found anyone or not. Now its being said more forcefully or its being said the same way but now being taken seriously.
It sounds like if don't have a full blown room mate type relationship now that that's where this is heading. I've read here about other couples having such an arrangement so that's not uncommon. I'm sure others can comment on how that works.
After a couple years in this dynamic, feeling the way you did, were you able to do, (for lack of a better phrase) "building life together stuff" ...house improvement projects, retirement planning, buying vacation property,(time share) insurance, estate planning, etc. etc?? It was impossible for me to get motivated on any projects even ones I had materials purchased and in hand.
Does your child know of these other outside relationships the two of you have ? Or rather to what extent is her knowledge ?
Why are you pissed off? at the long standing situation (her BF) or the suggestion that you need to invest more time and effort into your marriage to maintain the hierarchical relationship your wife thinks you should have with her?