I’ve dumped people in a way that may have seemed out of the blue to them. Just because it feels like you’re having a great time, it doesn’t mean the other person is feeling it as much. It’s like first dates. I’ve been on dates, chatted, laughed, no awkward silences - the perfect date. Then one or other of us says no to meeting again. Just because you have fun with someone it doesn’t mean you’re falling in love with them. And after 3 months, I’d be wanting to know that I was moving from liking to loving them.
in my experience, it can go like this. You meet someone, you fancy them, you like them, you think they’re interesting and funny, and you enjoy their company. There might be niggley little things you’re not so keen on, but you ignore them, because everything else seems good. You feel you’ve finally found a great person, you spend time with them, you emotionally invest in the relationship. But the niggley things are still there. You try and push them to the back of your mind, because by now you’ve met each others friends/family, made plans for a trip or whatever. You tell yourself you’re being silly. No point finding trivial faults with someone when everything else is great. You try and act normal with them, because you don’t want to raise these issues, as you’re hoping you can forget about them, so you don’t want to make an issue of it. But there’s a tipping point - suddenly you realise the niggles are real, and you feel dishonest if you continue the relationship, so you end it.
So as harsh as it sounds, by the time I break up with someone, I’ve been thinking about it for a while, and acting normal while I solidify the idea in my mind. I feel that is preferable to dumping them at the first sign of a minor problem, only to regret it a week later and want them back.