Sexuality is a spectrum and technically speaking few people(if any) are 100% straight. So, you could be far down enough on the scale that you're basically 90% straight or more but have that little bit of capacity for sexual interest in men too, just that it's to a small degree and further repressed by society and societal norms and stereotypes(especially when we're talking about men). At the same time, you could be more bisexual but again so repressed it just doesn't manifest or at least hasn't up until this point.

Personally I think human beings largely have the capacity to at least be curious about sex with the gender they're not primarily or basically attracted to. Studies/surveys seem to suggest it and also suggest that a surprising nr of people who are and consider themselves overwhelmingly straight, have had or would have sex with someone of the same gender out of curiosity. So it can also be that something triggered that curiosity in you and your brain perceives it as something exciting in that sense more than actual romantic/sexual attraction towards men.

A therapist could help you more especially since it seems you are from a religious background and surrounded by religious people and conservative views of that nature, which come with a lot of guilt and shame, which could have influenced how you perceive your sexuality.

To answer your questions directly, yes you can be basically straight but with some gay fantasies(again,that spectrum) and if you happen to end up feeling you're bisexual it isn't a problem if you don't tell anyone you don't feel comfortable sharing it with, the only problem is how your mental health is affected by not living your true self and accepting yourself.

Oh and you can know who you're attracted to even without having had sex with all genders. We all start out with zero sexual experience but sexual experience and sexuality are different things.