This one happened this past weekend. A little backstory and then the good stuff.
I had been in a relationship with an amazing girl for a few months now, and she was everything I'd ever wanted in a woman. Recently our sex life had been getting a little stale for a few reasons. I've been out of shape, she'd gained close to 30 pounds since we'd gotten together and had lost some of her physical appeal, and sex seemed more like a chore than an enjoyable experience with her. It's mostly my fault, admittedly, but I was having problems finding my sex drive with her. I'd been working on it though. Got a gym membership and started working on my cardio, getting my blood flow back up, and I've been doing a lot better about initiating sex with her. But she was still having confidence issues about it all and started suspecting I was getting some on the side.
I wasn't. I've been diligently faithful to this girl from the start.