If you aren't there at night or much of the time because you are at your boyfriend's, then she may feel entitled to do as she likes in the room.
I agree that getting headphones is a good idea. They don't have to be expensive.
I don't have room-mates but I have managed to live with my husband for 28 years. When he plays his X-box he uses head phones because I get tired of the noise.
When one of my daughters is home and at the computer they use headphones because they want to listen to music or episodes of Lost while I am trying to read.
In my world, if you are the one making the noise, you are the one that has to compromise.
Noise is like second hand smoke. It is disturbing and hard to get away from while quietly doing something only irritates the people who want to make noise.
I had (another) similar scenario in the summer, in case anyone remembers. After work, I'd always come home and want to practice my clarinet, but my brother would sometimes be watching TV in his room, which was next to mine, so I'd go downstairs and practice in the family room--which he also didn't like, because he'd tell me that after watching TV, he would want to use the computer, which was in there. So basically, he'd be telling me I couldn't practice in my room OR the family room. I could use the living room, but I didn't really like to, because it had carpeted floors, as opposed to the hardwood floors in the family room (which was actually my favourite room to practice in, except for the hassle of moving my stuff downstairs), which muffled my sound. In this case, yes, I was the one making the "noise," but when I posted about it on here, everyone unanimously said that my brother was being rude, not me, and I shouldn't have been the only one expected to "compromise." Oh, and sometimes, he'd expect me to vacate the family room when I was watching TV (he had one in his room, I didn't have cable in mine because our dog had chewed through the cable), because he wanted to use the computer in complete silence.