Getting attached is hard

I've learned that it's not safe to get attached to people, for they seem to always leave. But I did it. I got attached, and I feel that these people are going to disappear out of my life and I am no longer going to get that sense of happiness. This is the feeling that causes me pain, and right now I hate myself for getting attached to them. I never open myself up to those I have not been born and raised with. This time though I made an exception, and I feel it crumbling right in front of me. I don't want to go down that deep dark hole again. I want them to stay for good.