<human>: I [M, 27] have been with my gf [27] for 5 years, and we've always maintained a certain level of sexual activity, usually at least a few times each week. Starting about a month ago, that all changed. She began to act uncomfortable whenever I made advances, even becoming uncomfortable with kissing, so I backed off. I figured it would change with time.

It hasn't, and when I finally told her how unhappy I was with he fact that there was no longer any sexual contact, she told me she wasn't interested in it anymore. I felt hurt and didn't pursue the topic any further.

Earlier tonight, I got very upset after she started to make some comments (probably in jest) about wanting to have sex with an actor in the movie we were watching. She told me she doesn't want to feel that I'm for in her to have sex with me, and that she doesn't know why things have changed. I said I don't want that either, but it is important to me and that I need to feel like we are working towards a solution.

I don't feel like she is interested in dealing with it, though, and the whole situation has me feeling depressed and ashamed. How do can I talk to her about this when she seems so disinterested in addressing the issue? And, if we get to that point, how do we figure out what has made her feelings towards sex change?

Summarize the given text in a few sentences.
<bot>: My gf is no longer interested in sex but claims not to know what has changed. How do I talk to her about this despite her reluctance to do so, and how do we figure out what has happened?