I think you should think of it like this. Everyone is flawed but if you dwell on the negativity of yourself then everyone else will seem like their lives are going very smoothly which is probably not the case. It sounds like you're too accustomed to losing people that you seem to feel it's a common occurrence. Articulate how you're feeling to the ones closest to you, they probably feel that you're slipping away from them.
And always keep yourself occupied at the moment, any chance to overthink might affect you and if you're out there doing the things you love or trying out new things then maybe it'll break the shackles holding you back in life.