Is abandoning a coworker who has wronged me considered abandonment? And is he considered a brother in Islam?

Abandoning work due to a colleague is not among the forbidden types of abandonment (hajr), for hajr is the cessation of speaking and greeting upon meeting. You should strive to mend the relationship with this colleague and understand the reason for their displeasure with you, as perhaps you were mistaken in your assumption that they are harming you, or perhaps they had an excuse you are unaware of. You are not obliged to befriend them, but merely greeting them upon meeting is sufficient; for abandonment is lifted by it according to most scholars. If you are certain that communicating with them harms you, then there is no sin upon you in abandoning them. Brotherhood contradicts abandonment, except for the brotherhood of Islam that unites you both.