It's saddening to read about this. The simple answer is during the early days of dating people put on their best behaviour saying things they think their date wants to hear, agreeing with them a lot and so on. Perhaps at that point they sincerely believe it. No one sets out on a date without a willingness to engage
with the other person.
But then, of course, the repartie starts to dry up and their mundane selves start to show through. Men are notorious for needing a sense of conquest. I'm not being cynical. It could be that those mundane selves match quite well; that the people are collaborators, enjoy each other's company (and whatever else), and appreciate what each brings to the other's life; and continue with a loving relationship.
Sad it is to say that hasn't happened here. I know what it's like myself and misguidedly I'd once go on the rebound. It didn't assuage the pain, just led to more trouble.
I'd suggest you give yourself a little time to heal; develop an optimistic attitude (with affirmations if necessary, not about boys but optimism and brightness generally) and try not to develop romantic expectations of people you meet. For a relationship to work and feel content and joyous it's important to be friends as much as anything else, and sincere friendships take a little longer to develop.
Here's wishing you well and hopes for a quick recovery.