All of us are only so strong - both physically and emotionally. Some people can hold 500 pounds on their back, while others would be crushed by that weight.
We all also have an emotional limit as well. We feel suicidal when that limit is surpassed, it doesn't necessarily mean that person is weak or strong, it simply means that they personally have too much to carry.
Accusing people of selfishness is unhelpful to anyone who is at or near that point. Our duty to each other is to try and help someone when we see them with a burden too great, not to pass them by and call them weak.
Some people are exceptionally strong, I'm not sure anyone is infinitely strong, which means that most of us, given enough of a burden, can break. One thing I am absolutely certain of is that we all do much better when we carry our loads together.
My resentment from a loved one killing themselves would be that I hadn't been able to see that they were struggling or done enough to help with their load.