I hate to say it but it sounds like you have different priorities than your friends.

You did the right thing in reaching out to them to apologize and holding yourself accountable for your actions.

Unfortunately, it sounds like they value recreational drug use over a friendship. Seeing a friend have such an adverse reaction to a drug made them realize that there are risks that have the potential to escalate to something dangerous quickly.

They are understandably afraid to expose you to a situation that involves recreational drugs but aren't willing to change their behavior to continue your friendship. It sounds like they are make the decision to continue their lifestyle as-is and they don't want to learn from the experience.

That being said- I may be jumping to conclusions. Based on the way you described the situation- it does sound like it may have been traumatizing and it may take them six months before they feel comfortable. It may not hurt to reach out once a month through text just inviting them for coffee or a show- but you have to decide if you can be prepared to handle any potential rejection.

Focus on healing; finding new friendships is extremely hard and takes time.