Even in a non-judgemental family, this is not the easiest thing to do at 13, because a parent might be likely to blow it off and say you are too young to know, and that might hurt your feelings as much as hearing outright homophobic slurs. There are websites designed to help gay teens with issues like this, I'd search them out, and also contact PFLAG to see if there are resources there.
Pandabear, female adolescent sexuality is very "suggestible", meaning a lot of girls try out a lot of different roles. A lot of girls go through a phase where they have sex play with other girls. Especially a girl who has a lot of LGBT+ friends. A 13 year old boy who believes he is gay IS gay. A 13 year old girl who believes she is bi and has "crushes" on both girls and boys and has close connections to the LGBT+ community when she discovers this, is often just maturing and wading through social and sexual feelings. I don't know where you'll end up on the LBGT scale, but this is a time of growth for you. You might also become vegan during this time, or another lifestyle that is socially driven. If you had "many" friends who were wiccan it's likely you'd dabble in that, too. You're trying out your identity. I say this all not to poo-poo whatever sexuality you choose, but to caution you that this isn't worth wrecking your life right now. You are very vulnerable, and your mother lives with a guy that's homophobic. You are in an incredibly vulnerable spot. Don't throw yourself off a cliff on purpose. You don't have to verbalize every thought you have, honey. Take care of yourself, and don't purposely make your life miserable. However you turn out, is how you will turn out, but there's no reason to give this guy ammunition to harm you while your mother stands by and lets it happen.
As a parent who has a son who is transgender female to male and didn't quite accept it at first, I get why you're worried. My son came out when he was 13, and we did not quite accept him and made him go to a gender therapist, but after a few monrhs of realizing it's not a phase we accepted him. My wife had a tougher time with it than I did, as she's religious and it went against it, but she too learned to accept him.