Be sure your friend understands you aren't out yet and be prepared in case it somehow leaks out. If you have friends who know and friends who don't there's always the possibility someone will let something slip.

My son was accidentally outed on FB, someone posted something and somehow my mom saw it. I still wonder if one of my sisters didn't find out first and tell her.

I understand. I am bisexual, and know that I am. But I come from a very religious family, so coming out scares me. They had a big problem when my youngest brother came out as bi. :/

Find someone you feel safe with and tell them. You don’t owe anyone the truth unless you want that kind of peace of mind. I regret letting my family find out, but I told a few friends and it made me feel a lot better. Best of luck :)

I would tell her for sure. It sounds like she will be a good support to you. Do you trust her not to tell others?

Tell her. Life is far to short not to be truer to yourself and to not be who you wish to be. You are who you are and how you are and you need make no excuses for that.

She may be just the one that could ease you into telling your friends.

When we lie someone, or love someone we come to adore their heart, mind and soul-that is their essence and being. No matter how you relate or how you come out as that has not changed. If your friends liked you for those reasons they need to understand you are still you . Give them time. If they can't then they may not truly be good friends.

you are who you are - if they can accept you, then you know who they are

Ok here's my opinion. I am bisexual. I hid it for many years fearing judgement. This was my Revelation. I don't feel the need to tell anyone. My bisexuality is mine own. If someone asks me I will admit it however I do not go out of my way to advertise it. Good luck.
BTW I would confide in your friend who is involved in the LGBTQ movement on how best to come out.

Its definitely not an easy thing

Dunno why you should 'come out' just cos its the thing to do as dictated by the LBTBQ. You are your own individual and can kerp your own preferences private.