This creator put together a great take on how that last explosive conversation came to be, specifically within the lense of the discrepancy between Kyle and Amanda starting a family.
However when she said Kyle "took it on the chin" I had a moment where I flashed back to the season 7 reunion. For context, Danielle is in her feels over the Rad House proposal and during a break, a group of them are backstage wondering if Summer House will survive this and Kyle says "My strategy over the years has been to just fall on the sword and like forgive and forget."
If this has been Kyle's strategy for keeping the peace just for the sake of the show, then it's fair to think he brings this same strategy to his marriage to try and keep that same peace. His bursts of temper tantrums (not justifying, dude needs to better regulate) are when he gets overwhelmed to the point he refuses to fall on the sword in that moment. Once cooler or more sober heads prevail he's always seen coming back, tail between his legs, and apologizing to then move past the conflict quickly... because summer should be fun. This has created an environment for Amanda to never have to take accountability.
Kyle is not without faults, but when he is repeatedly being reminded of the shortcomings he thought they got past all while actually putting in the work to try and better himself/his relationships, frustration builds. Amanda sees that frustration, takes full advantage of it, and it's what we have now started to see as her M.O. being the perpetual victim. If Kyle is always wrong, Amanda gets off not having to take any accountability in her parts of the crumbling marriage.
Circling it back to the dinner explosion in the last episode, here we see the straw that breaks the camel's back, both Kyle and Amanda's masks fall. Kyle stops taking it on the chin, gets pushed into throwing full blame back at Amanda and gets a solid FU in there because he finally pieces together how she has been moving behind the scenes and speaking to others in the house. Mandy drops her mask by reveling in Kyle's explosion, barely being able to contain her excitement in thinking she got another "see what I have to deal with you guys" moment.
IMO, if it weren't for the Scamanda of it all this would have solidified Kyle even more as the drunk hot head, incapable of loving his wife for who she is, and another Peter Pan syndrome Bravolebrity who can't fathom giving up his current life to settle down.