My biggest core belief is definitely "I'm unlovable." It fits so perfectly into thinking that others only want me around when I have a use, and not because they care about me. Haven't really found a counter since I think, deep down, everyone does things subconsciously or consciously for their own needs. For instance, when people help me or are kind, it's because they want to gain my trust so I'll do things for them. I remember telling this to my boyfriend and having him say "How sad is it to think an act of kindness is selfish." It's really stuck with me.