The female menstrual cycle is unique to primates. I'm not sure how far this goes back and opened a question over at biology stackexchange.

But that's not everything. A human can get horny without feeling love. A human can feel love after chatting on a dating website and telling himself in his mind stories about how awesome it will be, to be with the other person.

While Bonobo's like having sex I doubt that they would be capable to fall in love like that. They ability to tell yourself that kind of story seems to be something very human and evolutionary recent.

Nature doesn't protect us from unilateraly falling in love through fantasizing about a person that isn't present.