it took 40 years of my life to finally come out as a lesbian.
it wasn't because i ever doubted my attraction to women and nonbinary people, but a combination of multiple factors:
1. compulsory heterosexuality had me firmly in its grip. i was even married to a whole-ass man for many years! now he and i are good friends and still live near each other. looking back on it, we would have worked out a lot better as cohabitating besties. after the divorce, i lept into another long-term relationship with a man, and that... was less good. (i'm polyamorous, so i also dated women and nonbinary people during those long-term relationships.) i wasn't even sure i was attracted to men at all. as someone with horrible self-loathing and body dysmorphia, i craved the validation of men's attraction to me. i felt like i couldn't say "no" to men, and i often "consented" to sex or play with men despite my lack of physical attraction to them.
2. lesbophobia from cishet society of course, but also from within the LGBTQ community itself-- the persistent stereotype that all lesbians are TERFs and all TERFs are lesbians. the bullshit idea that being a lesbian is inherently exclusionary and oppressive to trans and nonbinary people. the idea that lesbians can't even be attracted to nonbinary people, and can't be nonbinary themselves.
3. the ludicrously ahistorical position that lesbians cannot be transmasc or use any pronouns other than she/her. usually this came from severely insecure and dysphoric transmascs/men who claimed that transmasc lesbians who go by they/them or he/him were somehow delegitimizing their identities as men, as well as tainting lesbian identity itself. once i realized that tended to come from insufferable tankies who desperately need to touch grass, i was able to let go of that shame and self-doubt. i'm not "betraying" lesbians or non-lesbian transmascs by being both transmasc and a lesbian.
anyhow, i'm a big ol'...
there are lesbian resources and archives in my links!