My wife (as of last Saturday
) and I have been together for 6 and a half years, and I have been a tripper for all of it. For most of it I only tripped very occasionally, but for the past two or so years I tripped a hell of a lot, all things considered, and most of it she didn't know about. She's always known I tripped, and sometimes she's known during trips, but she tends to be weird about it even if she tries not to so generally I haven't told her and have just went on with the day without letting her know I'm tripping (but still spending time with her). I haven't done that very much since the new year. Over the years she has gotten much more open about it, until recently she said she intends to eat mushrooms with me one day, which is a huge step. But she suffers from anxiety and it could be either really good for her or really bad, so I'm glad she's cautious (about as cautious as it's possible to get, really). I don't feel good about all the hiding but at the same time she knows I do it sometimes and it's more of a lie of omission... not like with your girlfriend where she outright hates it.
The thing is, though, that we are able to talk about my experiences and she is also a very spiritual person who has always had pretty amazing experiences without drugs. So I can still share this part of my life with her.
Bottom line, in my mind: you need to decide which to choose, drugs or her. Do you feel ridiculed by her when you try to discuss your experiences? How does it make you feel? Does she ridicule you when the spirituality you discuss is not drug-related? If so, you should decide whether that's the kind of attitude you want to be around for the rest of your life.
If it's just the drugs, then maybe you should lay off of them if you want to keep her. Love is very important and if everything else is compatible with you two then maybe drugs should be less important to you than her.