There is no way to predict how your significant other will handle a breakup. Any breakup is emotionally wrecking, and seeing each other every day only makes it worse for everybody. I do not envy either of them.
Mr. Mateen's behavior is deplorable, but not exactly surprising. There are only a few ways to handle a breakup. Some are positive, some are negative, but this behavior is definitely on the list of possibilities. Ms. Wolfe should have recognized that risk when she went into business with her boyfriend.
In normal circumstances, she could just ignore him and he would (hopefully) cool off. But obviously she can't do that when she works closely with him.
When she began dating Mr. Mateen, there was a risk she would break up with him, and a subsequent risk he would act insane because of it. When she went into business with Mr. Mateen, she lost her options of mitigating that risk sacrificing her ability to ignore him in the event of emotional catastrophe.
This sucks for everybody involved, but especially for her.
This guy seems like a real piece of shit.
As shown by the first Ms. Wolfe was able to handle separating her breakup from her duties at work. She went into starting the company knowing she would be able to handle remaining professional at work if the relationship ended.
Mr. Mateen went into founding a company with his significant other and was clearly unable to handle separating the company from his relationship. This falls squarely on his shoulders.
Plenty of successful companies are built up around relationships. Plenty of companies survive their founders ending their relationship. While it is painful, they most frequently are able to work things out by being civil and being able to separate their relationship from their business. This all falls on Mr. Mateen's shoulders for not being able to separate the two.
To be clear: Ms. Wolfe is the obvious victim in this situation. She did nothing to deserve it, and all responsibility for it falls on the frail, slimy shoulders of Mr. Marteen. There is no way she could have predicted that he would act like this. However, she could have known it was a risk.
Furthermore, the fact that Mr. Marteen is 100% responsible for this situation does not invalidate my advice. I am merely pointing out the risks of starting a company (or joining one?) with your significant other. To paraphrase another HN commenter:
When the police teach people not to leave their keys in their car while they pump gas and go get a snack, is that victim blaming? No. It's advising people to consider the risks of their actions, which could unintentionally lead to a bad outcome.
In fact, I agree with you. He should definitely be gone, not her. She seems to enjoy Tinder the app/product/company, and were it not for him, she would still be there.
The reason that is not the case is because there is a systemic lack of HR or proper channel to report this behavior. But that's another discussion entirely. I'm simply saying it can be a bad idea to start/join a company with your significant other. That doesn't mean you shouldn't do it. But you should realize this is a risk.