lady, to answer your question to why doesn't love last, perhaps you've just not found that special someone.
it's not easy for many of us to keep ourselves away from black and white thinking..meaning we form opinions to the extreme rather than considering other thoughts or feelings. like letting shades of grey be considered. your feeling like you'll never find a long term realationship is an absolute thought rather than thinking it will/may happen for you, just not yet. try to keep your optional thinking open or you may miss that moment.
"doesn't matter anyways because I'm too ugly and self-conscious ..."
our self concepts can also be skewed. working on your self esteem may be helpful for you. here are some links that may help you...
http://www.mayoclinic.com/health/self-esteem/MH00129

http://www.livestrong.com/article/13925-self-esteem/