Child of divorce?

when i was 12 my parents got divorced cuz my dad cheated on my mom. he married that woman, but he cheated on her, and they got divorced when i was about 16. then he started dating another woman. me and her got along great, and i thought they would get married, but my dad cheated on her and they broke up when i was almost 19. then he met a woman online and they got engaged. Ive only met her once, and that was after they were engaged. I got married, and about 7 months later my dad got married. im so sick of my dad cheating on these women, and i dont even see the point of getting to know my new stepmom cuz i know their marriage wont last more than 4 years max. when they were dating my dad sang "Faithfully" by Journey to her. that really upsets me. why does he think he can be faithful to her? why are her kids enough? Im just so upset. it never used to bother me, but im just so tired of it. has anyone else been in this position? why is my dads marriage now upsetting me when the others didnt