Spent the snowstorm weekend with my sister

I spent this past weekend with my older sister. She is 7 years older than me. I've never really thought about her sexually before. It escalated quickly but we had sex 4 times over the weekend. I don't know why I kept doing it. But I now don't know what to say or do. We didn't really even talk about it. I have a serious gf and she is engaged. Like do we never talk about it? I feel super confused about the whole thing.

Anyone else kind of have something like this happen super randomly and quickly with a family member?