Threesome?

So. My baby daddy and I been together about 3 years we have a 2 year old daughter and a great relationship overall. We are both 22 years old. He’s like my best friend, I’ve never been so comfortable with someone. I feel comfortable trying new things with him sexually more than I ever have before, I feel safe. He one day brought up the idea today a threesome, but with two men. Honestly it peaked my interest… surprisingly. I feel like I can be very vanilla sometimes, but then again I haven’t slept w many people and I’m still learning and discovering new things I like. But I’m afraid of this ruining our relationship. I also am not against having sex with a girl, I never tried it and I’ve ALWAYS been curious about it, so I’m honestly down for both… I worry about how our relationship will be afterward. I’m secure with myself, but I would hate to find out he was sneaking around with someone we slept with together or accidentally falling for someone else. Tips? Experiences? Help a curious girl out! 😭 I really love him and this is a guy I’d definitely want to marry. I feel like him wanting a threesome doesn’t mean he doesn’t love me, I think a lot of people have this fantasy. But in the back of my mind I am kind of like “am I not enough… are you still attracted to ME?”