I think he died since I checked chapter 1 and when it talks about her, it shows her in funeral clothing holding a portrait but it says in the same frame "her heart has became toxic" so I think there is more to him just dying.
Yeah, don't bring that kind of thing up with a kid without discussing it with the parent first. Puts kids through an emotional rollercoaster. You'll invoke protective mama bear mode quick.
MC did deserve this since he not only did that with ulterior motives but he also skipped the asking for the kid's mom's permission to do the cooking class thing. Sure she had the right to get mad at him but not to the point of being all psycho mother bear.
Now the questions here are ¿why did she get mad at her kid asking her about the dad IF he is supposed to be dead? Also, why if the father is dead did the kid say he wanted to spend more time with him? Why keep quiet about the father's death if he is actually dead?
I think there is more to that MILF than the author is letting us know. And given that MC hasn't let go of her even after knowing that she already got married and has a child the story in my opinion is going to be about how MC and the MILF one way or another get together in the end leaving the dick loving sisters and the manager heartbroken as well as the other possible women that will appear later in the story...