Conflicted Consent in Law School

So yeah, I’m a first-year law student and we’ve been in this open relationship thing since the start of school. It’s not like it’s some kind of secret or anything, most people around here get that you can’t really have a monogamous relationship while trying to build your career path. But there’s been this one night recently... My partner, let's call her Sarah, was out of town on business and I was having trouble concentrating in my classes because she hadn't called all day. Late at night, I got a text from Mark, he’s not even an official part of the arrangement, but he keeps showing up when we’re both down for it. He suggested meeting at his place to talk...and maybe more. It felt like too many emotions were piling up inside me and I needed release. So yeah, I went. We ended up in bed together pretty quick, not some slow dance, just straight to the point. Sarah’s been out of town a lot lately, and I miss having someone touch me...even if it was Mark. He kept telling me how much he wanted to make me feel good, but I couldn’t get her off my mind. I know it sounds messed up...but then again, we’re talking about law school here, right? And honestly, I don't regret any of it, the release was exactly what I needed after all that stress. Maybe I’ll talk to Sarah about it later...or maybe not. Whatever, she knows our deal works both ways.