My fiancé was with men before me

I found out just over a year ago that my now fiancé thought he was gay before we met. He had been with women but strongly preferred men. He kept this a secret for a very long time and then I managed to pull it out of him when we were talking one night. At first I was in shock because I did not see it coming. Since then I’ve gone back and forth with my emotions on it. I am not homophobic at all- in fact I am bisexual myself and I’ve been with other bisexual men in the past with no issue. I think what really gets me is that he kept it secret for so long. I understand he wasn’t out so it was a very private thing for him but we were very close even before he told me. His friends knew way before I did. Anyway, I’ve mostly come to terms with it but I find myself feeling super insecure because I wonder if he misses men or if he’s actually gay and will one day leave me for a man. I wonder if he’s completely satisfied with me or if he’s lying to himself. He seems to never show any interest to other women which don’t get me wrong, I LOVE. But I’m wondering if this is because he simply doesn’t like women? Like I’m an exception? I don’t doubt he loves me. And he is sexually attracted to me. He insists he’s not gay or even bisexual and that it was just a phase. Please don’t come for my throat on this one. Like I said, I’m not homophobic but it’s hard to imagine the love of my life being with men before me. And I understand that there is a double standard since I was also with women before him. I know he’s not in the wrong but it just makes me so so insecure even though he’s never had a serious relationship before me and our love is so strong. I guess I’m just wondering if anybody else has experienced this or if anybody who has a similar story to his could speak on the issue. Just looking for reassurance I guess.