Hey there!
I took the beginner's yoga class last winter term and really enjoyed it. Have you ever done yoga before? You don't need any experience but I have a bit and it did help because I knew what to expect when the instructor named a pose. However, like I said, you need no experience. In fact, there were quite a few people in the class who'd never done yoga before.
The class introduces basic yoga poses. What I liked is that the instructor will show you a basic pose, allow the class to try it, and then show you a more advanced version of the pose to try if you are comfortable doing so. It's really work at your own pace with respect to your level of flexibility and familiarity with your own physical limits.
The class is also a great way to unwind once each week. The instructor had a calm voice and I found doing the poses kind of helped drain out the stress of school.
As for the gender composition of the class, it really was female dominant. There was probably one or two regulars who were guys, and every now and then a guy would somehow drop in for a class. It's a really relaxed environment, so the only way it would be awkward is if your boyfriend made himself feel awkward. I wouldn't worry about that part too much