Bob commits suicide after losing Alice, both of his parents, and several close friends in the same week.
Bob kills himself since Alice no longer loves him and he has no one left to live for.
Bob suffers from depression; losing Alice was the last straw in his long battle with his psyche, and he sees no other way out.
Alice had an actual magic aura that caused Bob's pain to ease whenever they were together, and Bob found quickly that he was in love with Alice. Now that the pain is back, he can't stand both it and losing Alice.
The character is a masochist who literally lives to suffer.
A character ends his suffering by killing himself after settling his affairs. The character makes his death seem like an accident so his loved ones would not feel guilty for his suffering (and/or to make sure the insurance policy on him gets paid out).
Played For Drama: Bob is totally depressed due to how people dismiss his claims of having problems, even by his own loved ones. As he chooses to take his life, this causes others to vehemently point out that Bob has really crossed the Moral Event Horizon.