Gf's sex drive is down, how can i help?

Talk to her: Find out if she is worried about something or not feeling well. Also try and talk about how things are going in your relationship. Are there any conflicts over common issues such as getting married or having children? Any of these things could be affecting her sex drive. Also, any new medications could be a factor. Don't push if she doesn't want to talk about it right away, but keep trying.