How do I tell my gf I’m gay

So for context I’m a man dating a girl and we’ve been together for almost 5 months. I was identifying as bisexual when we got together and had been for almost a year. She knows this about me. However the past couple of months I’ve been very confused but I’ve I’m pretty sure I’m gay and I know I need to be honest with her. I’ve tried to bring it up, but every time I get too scared. I’m worried about her reaction as she really wants us to be together forever and talks about our future so fondly. I care about her so much that I don’t want to upset her but not telling her isn’t an option obviously and I can’t keep dragging it out. I know it’ll hurt her, but I can’t help the way I feel. I think it makes it harder as my family really like her too and also idk what reason I’d tell them we broke up as I’m not ready to be out as gay to my family. Has anyone else been in a similar situation? How did it go? I’m so worried

UPDATE: So I did it. I told her the truth. It was so nerve wracking but I told a close friend who supported me through it. Obviously she was upset but happy I told her and was honest. She said she’s thought something was off with me so it makes sense. I feel a weight lifted off me. I’m so thankful for everyone who commented their stories and advice. I feel really sad that she is sad and heart broken but it went a lot more smoothly than I expected.