I don’t understand it

You can surely fall in love without loving yourself, but the thing is, your lack of love for yourself might get in the way. Like hiohneh said there’s always people that can take advantage of that. There’s also people that do enter a relationship without self-love but end up developing it thanks to the person they are with, but t’s usually the other way around (lack of self-love hurts the relationship).

I might be greatly wrong about this but happiness to me are just temporary moments, i’d take having peace with myself and my life situations over being happy every time (and i do think plenty of people get confused about those). You can get happiness from a random event, a person, a hobby, etc, but you can’t be at peace with yourself out of anything but soul searching (and in the long run it’s a lot more useful).