Why can't we be selfish?

Those who commit/attempt suicide get a lot of crap. People say it's selfish and all you do is hurt others. That is true, suicide is selfish and hurts other, but why should we put others before ourselves? Isn't selfish to demand that someone who is hurting stay alive just so you won't be sad? And depression isn't always treatable/curable, so in many cases people want you to stay alive even though you'll always be in pain. I've talked with a few people who have had depression for 40+ years, they've taken medications, talked with counselors, and nothing worked. It's not my intention to hurt those around me, but I'm not gonna be miserable just so they won't be sad. Yes it's selfish, but it's my life.