Reinterpreting positive Situations into negative

I have this so often, that when people smile at me, I feel happy because of it. Then later in the day something bad happens and I start to think that these people didn't smile at me in a positive way, but because they found me pathetic or laughed at me. It makes me spiral into negative thoughts. I know that black and white thinking is wrong, but it's still very difficult for me to integrate, that people have different opinions of you. Sometimes I radiate positive feelings and have a good self esteem and people smile at me. Later that day something triggers me and I see everything in a completely different light. It makes me want to hold grudges and isolate. I know this sounds narcissistic, but I try everything to not be one. It's like I have the triggers of a narcissist without the bad stuff like manipulation. How can I ever live a happy life when I am so easily being brought out of my Center? It's so easy to slide into an bad relationship. It's so easy to get into the wrong friendships. Why is it so hard to find the positive stuff? People that build you up or real friends? There are days or moments when I think I have it together, just to feel like I am spiralling and see everything in a total different light? It feels like BPD sometimes (although I would never say I have it, these people suffer REALLY BAD), and it all comes from a deep distortion of my ability to trust myself and other people. It's like I am carrying all these fragmented parts of myself around, and people react to it. Sometimes this part of me, sometimes that part of me, and these parts aren't wrong or right , it's just that they fluctuate in me and they don't stay, they go and come like my mood. It's just that I can't handle negative triggers very well. I am happy and then something stupid happens, and suddenly everyone is a threat. Everything is too much suddenly. Its like my brain is confused which side of reality it should trust.