Why was Yaakov always afraid?
He may have just had a lot to be fearful of however almost every time we encounter Yaakov he is either nervous or concerned that something bad may happen. By the berachos with getting caught (Bereishis 27). When leaving for Charan he is reassured by God that he'll be protected until returning and responds with "should that happen and you'll be my God / then you'll be my God etc" (ibid 28). Upon returning and meeting Esav (ibid 32). When Shimon and Levi destroy Shechem (ibid 34). When the brothers are grazing the flocks at Shechem (ibid 37). When Binyamin needs to be sent to Mitzrayim (ibid 43). HaShem reassures him on the way down to Mitzrayim telling him that he needn't be fearful (ibid 46). Asks sons to bury him in mearas hamachpelah even though Yosef swore to that effect already (ibid 49). The Talmud says that the fear from Esav—despite his having been promised safe return—was due to Yaakov's fear of sin potentially undoing the prophecy (Bavli berachos