This might sound like a stupid question, and I know it's a little subjective, but almost every girl I date ends up having a meltdown of some kind several months into the relationship, sometimes weeks. It's hard to say exactly what I mean by a meltdown, but basically they get really upset about something (or nothing?) and think and behave super irrationally to the point I feel like they're being bonafide crazy, and literally nothing I do or say has any positive effect. To me and the way I am, the way I behave and live my life, their behavior is borderline insane (seriously; not trying to exaggerate or be funny), and honestly, the first few girls I dated, I genuinely thought they did have significant mental problems because of these meltdowns, but over the years I've learned that it's almost every woman. It's part of why I've preferred being mostly single the last few years.
I also ask because I'm currently in a relationship with a girl who is fantastic most of the time, but generally about one day per week she's pretty upset for no real reason at all, or if there is supposedly a reason, she drastically overreacts to it to the point it's clear to me she's just in a really bad mood that day; whatever stimulus there was could have been anything. There has also been two occasions now in the last 2 months where she's gotten so angry she's stormed out of the room and refused to speak to me for at least a few hours, and these were times when I was completely calm, did not raise my voice, didn't even know what she was upset about the first time and only vaguely the second.
Most relationships I've been in end up with me feeling like I'm taking care of an emotional 5-year-old, and it's hard for me to have respect for someone who I think is behaving like an emotional 5-year-old.