Not exactly stress, just a bit confused

So I finally broke a 20+ year streak of being single. I kind of reserved this idea for a full on girlfriend and I don't think I have that...yet... Anyways, I met this girl an hour away at an arcade and she came up to me and I think she spoke first but she was quickly on to me. She even said twice "i'm flirting with you I hope that's ok?" 
We hung out all night I didn't get back till 5 am. So it's been a really long time, and I see things slowed down after the first meeting. Maybe it's just my opinion of it being too slow? She is in an open relationship (so I believe there is another guy) and I am not her first guy for that situation. I was ok with being with her, and still am but I feel like I am just 3rd wheel. I know it's only been a couple weeks, but I want to jump on this opportunity hard. I feel like if I let this go I will be hard single again. So I am not sure how hard to press it. She asked me to call her today and we had a very good conversation, and maybe she is unsure how to juggle 2 relationships? What to do? I really like her.