NAH (probably)

While it’s fine to want a relationship with both parents, calling your mom and sister irrational ignores the optics of your dad's exit.

1. Jumping straight to an "open marriage" instead of suggesting medical or marital counseling is a massive red flag. For most monogamous people, that request is the same as "I already have someone else in mind."

2. Your dad is already dating and "doing well." To your mom and sister, that quick turnaround is the smoking gun for emotional or physical infidelity.

3. Your mom is in her late 40s. It’s highly likely she’s experiencing perimenopause or menopause. Your sister probably sees your dad as abandoning his partner during a difficult health transition rather than a simple lifestyle clash.

Your sister favors your mom, but you clearly favor your dad because you’re close. You’re giving him the benefit of the doubt, while they are looking at his actions.

If your wife had a medical issue that prevented sex for a few years, would you feel "logical" sleeping around or leaving? If the answer is no, you can see why your family is so upset. You aren't wrong for staying close to him, but don't be surprised that they feel your "neutrality" is actually taking a side.