Hi guys!

I'm hoping to hear advice and opinions on a situation I am having.
I have been dating my girlfriend for 4 years. We are in a serious relationship. In the beginning we had a serious issue. My girlfriend was used to a lifestyle surrounded with drugs. Ecstasy but mainly coke. When getting serious, about 5 months in I told her how strongly I felt about the use of coke. I have a strong opinion on drugs and it is something I won't want around in a relationship specially for my partner to do. I asked for her to stop doing drugs. I had a previous background of occasionally smoking weed. In return, she asked of me to stop too so we both did.

This is a subject we never talk about. About a year ago I asked her if she missed drugs. She responded saying normal, she doesn't want it but ocassionaly thinks about it. This is something that has been bothering me for so long because of my paranoia but never talk about.

Last week I asked her if she's done it with her close friend that regularly does it. I asked if Drugs have ever been brought to our apartment. She said no. But I asked, and she did admit to talking about it with her friend, admitting that she misses it and she would want to do it. She says she has to keep that from me because she knows how strongly I feel about drugs, so she can not talk about that in front of me. I am not mad at her. I am glad she was able to tell me the truth. But ever since having this conversation with her I've been extremely sad and feeling down because I thought for so long she didn't think about it, she didn't want anything to do with that lifestyle until now.

Now I find out she still craves it. And the reason she stopped was to make our relationship work, not because she's over it. I do give her credit for being good to me. I can not change who she is, what she thinks of... but it is a lot for me to take in. But she thinks I am being extremely dramatic about it. I tried talking about it to her and she always makes comments saying it is not the end of the world and that she hasn't done it. Which yes, this is true. But is it okay for me to feel concerned, scared, and sad as bad as I am? I am very serious about her at the moment and finding this out sort of crushed me...
I am trying to let it go but I am just hurt. Is it okay for me to feel the way I am feeling?