Evolutionists/atheists: can you explain why certain behavioral traits such as jealousy and suicide are almost exclusive to humans? For what purpose

jealous is as natural as reproduction and is no way exclusively human. wanting what the other has and being angry if someone else has sex with the female that you want are directly linked with survival of the fittest because it stimulates inner-species competition which eliminates the weak and assures that only the strongest survive. most primates have all of these traits and hierarchy within primate groups has all to do with controlling access resources and who gets to reproduce.
as for suicide, its a bit more complicated. since humans are less dependent on fixed patterned behavior and more on learned strategies of survival we create plans in our heads basically and we execute them. with this new way of generating adapted behaviors the brain had to develop a plan B, a way to abandon a behavior if its not working. we have chemicals in our heads which are specifically made to demotivate us so that if a behavior is interpreted as leading nowhere we can "get discouraged" and " lose drive and desire" for a period so we can then create a new plan. sometimes our ideas get confused or our brain is a bit defective and then this mechanism goes rogue and causes what we call "depression" . depression is the brain getting stuck at the first stage of change: giving up, stopping what you are doing. suicide is the BIG giving up, its the brain not able to reboot after a "giving up" phase.
if you look at animal behavior, their behavior can be compared to a quasi-mindless obsession. squirrels cant stop burying nuts, they don't know why, they are just compelled to do so ,they happen to love it, and accidently, this leads to survival. this is how most of the animal world works. the human mind can generate such "obsessions", a man can spend 16 hours a day sculpting. but if this new self-created behavior ends up jeopardizing survival there needs to be an abort behavior button. so yes, I have never found a behavior that cannot be explained by natural selection but have found a long list of things that don't make sense in the christian perspective of things.

Evolving in evolutionary biology does not necessitate a purpose. It's not always for the better. It is simply change due to the environment.

Jealousy is a useful trait because it encourages resource guarding whether that be food, shelter or mates.
Suicided is, i suspect, a non-selected bi-product of the complex intelligence we enjoy.
It's not adaptive but not sufficiently maladaptive to be totally expunged.

These traits are off shoots of sentient behaviour. The level of self awareness that allows us to question ourselves.. No other living being is aware of its own mortality. No other being possesses envy or greed. (And your cat being fat doesnt count.)😷

Animals can be extremely jealous

Suicide maybe but definitely not jealousy. Dogs get super jealous. Animals do get depressed if isolated and not given mental stimulation, or food.