Two different perspectives

Em and I had a conversation the other day that resulted from a bunch of other topics that ran into several tangents (not an unusual occurence for either of us). It started with us talking about her boyfriend, and how he always seemed so excited when he made plans with other people. Here's how the conversation progressed:

Em: But see, he's not really that way. Sometimes he seems excited because the other person is excited. But he could really care less.
Me: Really? I hate people like that. I'd rather know where I stand with people. I think about that sometimes with my brother-in-law. He's one of those really nice people who gets along with everyone. I've even seen him being nice to people who I know he doesn't like.
Em: But that's just called being polite.
Me: Maybe, but it always makes me wonder. Like when my dad is in town, and he's talking to my brother-in-law. Now I love my dad, but he can tend to talk a lot about nothing (yes, yes, I know, I do too ... I understand that I'm calling the kettle black ... oh, be quiet and let me tell the story). I always wonder when I see my brother-in-law talking to my dad, whether he's thinking, "Will this man ever be quiet?" He doesn't look that way. He always seems interested in what my dad has to say, but he's a nice guy, so I wonder.
Em: He probably really likes your dad. I wouldn't worry about it.
Me: Yeah, but you never know with people like that, right? I always wonder when people are nice to me, whether they really like me or not. Or do they talk about me after I leave, and say how annoying I am. (The bad part about this statement is that I'm so guilty of it myself. There are some people who I can't stand, but I find myself being nice to them to their face. I guess that's why I feel so insecure).
Em: I don't worry about that. I feel like, if they don't like me, at least they respected me enough to be nice to my face.
Me: Wow, I never thought about it that way.

Em teaches me a lot about looking at things in a better light. I think I need to be less insecure, and more confident. And maybe just a little less hypocritical by being a little more honest with other people. But how do I do that? Do I just stop talking about them behind their back, or do I just be really mean to their face? Or is it just human nature to do that? Is it just part of being civilized that we are cordial with each other? But how do I tell the difference between someone who's just cordial to me, and someone who wants to be my friend?

It's weird, but I'm always surprised when I learn that someone new that I meet actually likes me as a person. I don't think I'm that special. Sometimes I make people laugh, sometimes I can tell a good story or two, sometimes I can help people out of a jam. But nothing out of the ordinary. I feel like I'm the clingy one, the girl on the outside trying to fit into the popular group. I'm always afraid to ask someone new to make plans, because of the fear that they'll say "What? I was just being nice to you because we work together," or something along those lines. Maybe I should just take Em's perspective and just remember that at least they respected me enough to be nice in the first place.