How can I make someone see that they are causing their own problems?

Mom mother is always sad.. Always having a “bad day”.. A lot of things contribute to it like financial problems, relationship problems and so on… You may be like, “I feel bad for her”, but shes always upset about something ALL THE TIME!! Its like the things that are going good for her she doesnt appreciate, she just focuses on the bad.. I, like many other people go through things as well, but I get over it & when something good happens I appreciate it and live in that moment.. Now heres the really bad part.. All the unfortunate things that happen to her, SHE CAUSES… Like with her relationship problems shes obsessed with this guy who was like a “childhood sweetheart” for her, I guess there was something between them years ago, but now hes been married 3 times and newly divorced and he doesnt want to date.. & my mother has been in 1 marriage and has been divorced for some years now and she wants to date that one guy.. He doesnt want a relationship, yet she continues to go after him, then when he tells her he doesnt want to be in a relationship like that, she gets all depressed.. Its like, you knew he didnt want something like that, why the hell do you keep going after him?!? Your only hurting yourself.. Its getting to the point where I dont like to be around her cause shes always sad, and being around someone like that is annoying.. What can I do? Ive already tried talking to her, but nothing seems to benefit that..