Why do people have abortions rather than give the children up for adoption? There is a strong, "If I can't have it, nobody can." can streak in some people. I suspect that there was more going on here than a mere request for a divorce, possibly the threat of, "I'll take the children, pets, and house and you'll get nothing." The wife going out with her friends may or may not be part of it, too. I don't think we are getting the whole story here.
Note that I'm not justifying the death of the kids or the pets. I'm explaining what I think happened, especially in light of an earlier thread about men killing themselves and having their lives ruined with child support payments and such.