I see myself in a lot of this. It seems to me that you have a default position of not only just not trusting people, but actively mistrusting them. Sure, trust should be earned, but with simple things like seeming excited to see you, it might be best to try to train yourself to give them the benefit of the doubt. Some people might seem excited simply because they haven't seen you in a while. I'm not that way, and you apparently aren't either, but one of the more important things you can accept is that people are vastly different from each other, and what seems outlandish to you may be normal to others.

I've had one close friend my entire life, and I just met them a little less than a year ago. I don't know why it took me so long, but I think it comes down to the fact that we helped each other out with some things, had a good amount in common, and opened up to talk about real things. That last one I've always had problems with, and seems to me to be what cemented our relationship, finding out we had even more in common. One of the things we've talked about is pretty much this exact topic, and by talking about it and other things, we became closer. They live in another country, and it's possible I'll never even meet them in person, but even without that, opening up to them was probably the best thing I ever did.

Some people might actually have some selfish motivation for seeming happy to see you, but I think in most cases it's more likely that's just how a lot of people respond when they see someone they know, especially if they haven't seen you in a while. If you start giving people the benefit of the doubt more often, I think you'll eventually find someone who's trustworthy, who you can talk to about some of these things, who will reciprocate, and you can both be yourselves, and rather than feeling pressure to continue or deepen the friendship, it will just feel natural. That's been my experience, at least, in my extensive history of having one close friend. :P