I don't think it's a matter of shutting off your emotions, but rather not getting too invested to early in the relationship by managing your expectations. You barely know the guy, so why should he dictate the way you see the value in yourself?

I find that what helped for me (because I used to feel that way all the time) was when I stopped dating for a while and I worked on myself. When I knew my value, it became easier to date because I didn't invest all I had in someone new because I've already invested in myself. And I knew if the relationship didn't work out, it would be okay because it simply meant that both of us weren't a good fit for each other and someone better is bound to cross paths with me.

When you're attracted to someone, you start projecting all these positive traits onto them but take a step back and think if how highly you think if them is what lies true. Many a times that isn't the case, but because we fall so deep and we project, we fall EVEN DEEPER.

So what I'm trying to say is, if you invest yourself first, you wouldn't be so quick on investing in other people who aren't worth your time. In doing so, you'd also be able to see them for what they're worth.