There's no way to twist it. You cheated dude. Drugs or not, you made the choice to break your vows with your wife and you deserve to suffer the consequences of your actions. The longer you wait to tell your wife, the worse it'll be, I promise. Call her if you have to, come completely clean or just show her the post because you'll have to start at the beginning of you want her to even attempt to understand it was 100% the drugs.

If it were me, you'd have to give that up and do marriage counseling to even begin to start to rebuild that trust, because she won't trust you at all, probably for a long time.