Why am I always forgotten by people I'm close to?

Every single time I am happy with a girlfriend, or a best friend, something changes and I'm always thrown away from their life like i'm nothing. One example, I had a best friend who I was extremely close to, her and I talked every day about everything, things were great and I was happy. Then one random day she just... stops and ignores me like we had nothing! Recently I got a great girlfriend and she loved me so much, we had so much fun together, then she just breaks up with me because she "Cant handle a relationship right now" because of family problems (I don't know if this was just a nice way to let me off or not) And now she just threw me away from her life as well even though she loved me a lot... Why must people change so much and do this to me? I feel like I don't even exist anymore