TL;DR, non-lgbt supporter realizes they’re bisexual and needs help, more details below

You're not the first person in the history of people to realize you were one way and not another—and you may have held back from being a full supporter of LGBTQ+ folks because deep down it concerned you.

Live your life, of course, and treat people well, regardless of their wedding tackle.

As for your mother, since I am not LGBTQ+ myself, about the only things I can tell you are to seek out support groups (online or locally, like via FB or Meetup or the like) and/or Google how to come out to an unsupportive parent. This is one of the first hits I found, and it looks to be a well-thought-out article: https://www.wikihow.com/Come-Out-to-Your-Parents

Best of luck to you, and good for you for understanding who you really are. Not everyone does!