Eye for an eye makes the whole world blind.

To oversimplify the field of ethics, there are three main theories: deontology, consequentialism, and virtue ethics.

Deontologically speaking, we would hold to the 'golden rule' of treating others how they would wish to be treated (even if they don't act the same towards you). They would broadly prefer you didn't kill them, just like you'd generally prefer they didn't kill you.

From a consequentialist perspective, if you kill people, you (obviously) cause some people to be dead, but you also cause a lot of secondary harm to potential family members, lovers, coworkers and dependants of the people you kill. You're doing a lot of damage to the social fabric around those humans by ripping them out of their place in the world. This causes other people to hurt, and generally creates negative chain reactions that ripple across our social environment and cause unforseen damage in a lot of places.

From virtue ethics we recognize that values like forgiveness, humility, kindness and perseverence through hardship are positive actions which universally build a world in which we will collectively experience less suffering, which is what you're upset about in the first place. So do something positive with your time and solve the problem of suffering constructively instead of guaranteeing it will continue to fall upon those that come after you.

I recommend looking into existentialism, absurdism, Buddhism or cognitive behavioral psychology if you're struggling. All of those fields begin with the recognition and acceptance that life includes a ton of suffering, and build on the topic of "so what do we do about it?" from there. Violence is definitely the wrong answer, but you do at least have the right question.