Since 2001 i have lost the first three loves of my life, in 2006 i lost my sister to death. im only 40 yrs old

im not understanding all that is happening in my life, or even why. when i was 15 i meet a girl name donna we were together until i was 23. husband killed her n feb (2003.) my best friend in the whole world i loved him to noend dies in dec.(2001) my second girlfriend whom i was with from 23 yrs. till 29yrs old. died last weds. (2008) my sister pasted in april at 42yrs old in (2006) can anyone give some type of expla. for what is happening