Feeling dumb

So my bf and I broke up(he broke up with me). The thing is he took my virginity and the way he left was just heartless: he said " so the thing is me and my girl are trying to make our relationship work so I can't be involved with u." I was like OK cool, but it broke me. All I keep thinking about is him and everything he told he and how it was a lie. Just don't understand because I was gonna leave him before I got to attached but he was like no I really like u, and ur different.

How could someone do that to somebody they claimed they like so much?

I just keep thinking how could i be so dumb to not even see that he was using me like that.

Yet still I miss him so much

Ps. His girl is his ex .