Am I Crossing the Line?

I dated this girl for almost 3 years, and we were on/off again for a year or so. We had a period of no contact, but we have remained friends and to be honest it kind of feels like we've never had closure or stopped thinking of one another.

We haven't seen each other or talked for a while, and she texts me the other day. She currently has a boyfriend i might add. We got to talking and I asked her if she wanted to grab coffee sometime (totally intended to be friendly, daytime meeting). She says, "yeah maybe sometime next week, but it would have to be our secret." So I asked her if she was sure, or if it was wrong because I honestly don't want to step on any toes or disrespect her current relationship. Her response was, "it depends on what I want to talk about there." I asked what she meant by that and she said never mind at first, but then she's like, "I just have a boyfriend so it has to be friendly." I already knew this obviously. Was she not thinking the same? Clearly it would be friendly, but it almost sounded like that would be hassel or something? Would it be wrong if we decided to hang out?

By the way, I know it appears that she is/was a cheater, but she really is not. We just have history and our relationship kind of wasn't resolved but it is? It's confusing. I guess the issue here is that I do have some feelings still, but I can't figure out if it's because I'm still in love with her or because I haven't been in another serious relationship since, although I have been with other women. I am not going to try and "get her back" on this or anything, I intend to be friendly and casual the entire time, but I can't help but notice how the comments sparked my interest. What does it look like to you guys?

I don't think you should go. Don't risk getting messed up in a situation you would be uncomfortable in. Would you like it if your girlfriend had a secret encounter with a guy she used to sleep with? Would you have a secret encounter with a girl you used to sleep with, if you were in a relationship? If she actually had just friendly intentions, she wouldn't have to keep anything a secret. Text her that you can't make it and cut contact.