<human>: So I broke up with my GF about a month ago, and we had little contact in the immediate aftermath. She sent me a few texts, but otherwise seemed to keep her distance. Last week, she asked (almost begged?) me to come over for sex, and after a quick exchange where she made it clear that she wasn't trying to get back with me, I agreed. (I didn't like the idea a lot since I figured this would have some emotional implications, but she was adamant that this was NSA sex, and I am willing to take her at her word)  We didn't use condoms while dating, and neither one of us has slept with anyone else since, so we didn't use them last week, either.

Fast forward to this past weekend, I end up hooking up with a friend of a friend (with condom), not important in and of itself, but it makes things a bit more complicated:

The ex/FB has been sending my texts for the last few days asking me to come over again, and I'm game, but this time since I've been with someone else, I feel like responsibility dictates I wear a condom even though I'm 99% sure the person I slept with this past weekend is STD-free. It's just not right to force that risk on someone else (agreed?). 

Problem: if I walk in and tell my ex/FB that I'm going to use a condom, she's going to know something's up. Should I expect drama to unfold? Does she have a right to be angry? I don't plan to tell her the gory details, something more like "since we're not exclusive anymore, I don't think we should have unprotected sex" but she's a smart girl, she'll know there's something else going on. Just looking for some insight.

Provide a brief overview of the text.
<bot>: Started hooking up with ex, but need to bring it to her attention that she's not the only one I'm sleeping with. How to bring this up?