Why didn't Avraham tell that Sarai was his wife? thank you

ב"ה Shalom The answer to this question is written is written explicitly in the Torah. Avraham was afraid, that if he were to tell them that Sara is his wife that would kill him. (Bereshit 12:12). That was because she was outstandingly beautiful among the women in Egypt and they would take her from Avraham after disposing of Avraham. According to the Netziv, in Ha'amek Davar a commentary on the Torah, Avraham's idea was, that if he tells then Sara is his sister, he would at least stay alive and try to save her from them. All the best