What even went wrong?

I went on a couple of dates with this guy and it seemed to be going really well, but without even knowing if I was feeling the same, he started talking about how he wanted to introduce me to his family and tried convincing me to consider him for marriage sometime. (He wasn't just saying he was looking for someone to marry). At one point we got into an argument on and realised we had different views.

Then on the next date, he strangely told me that he liked someone else and only 'assumed' she didn't like him back, but that she seemingly does, he wanted to end things with me. I was completely confused, I asked how he was really interested in me and pursued me just based on an assumption that she didn't like him, why not confirm that he had no chance with her in the first place? But he didn't reply.

What even went wrong?
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