Unsure what to do?

This isn’t one of those “I watch lesbian porn so I think I’m a lesbian” it’s so much more than that. That’s how it started. When I was younger I’d get nervous around other girls changing like in p.e. My friends should practice kissing with each other and I would steer clear. It all made me awkward. I couldn’t even sleep over at a friends house because of how nervous I was. Now fast forward to high school with my first boyfriend I’ve had a few and we’ve had sex but I’ve never been into it like them. Like I’ll be into it at first and have so many feelings for them and they just go away. I’m with my current boyfriend of 2 going on 3 years and we have a child. But he seems to think I like girls. And I’ve never confronted the thought before until he brought it up. And lately I’ve been fantasizing more and more about girls. But I’m so scared to do anything about it. I don’t want to end my relationship. And my family isn’t the most accepting. Ik they’d love and accept me but they make comments now negatively and it scares me to think if I am that they’d think those things of me. I thought about a threesome just to experience it and see if it’s all in my head. But I’ve heard they ruin relationships. We’ve talked about an open relationship but I wouldn’t be okay with that either. I almost want to do it with a girl and see if I like it but that would be wrong to my boyfriend. I’m so confused.