Second time hiding drugs, last straw? Or how do i tough love? (M23 & F22)

• I hate liars more than drugs -2nd time SO has hid doing hallucinogenic drugs from me
• most recent time: after much much tears and discussion, I was kinda okay with him doing LSD in this special one time setting with his close friends, as long as he only did 200ug -i get a call during his trip, he took 600ug, and he's not having the greatest time
• I find out the reason he did 6 doses oposed to two is because they had done shrooms the day before -2 ish years ago he hid doing shrooms, when I found out I told him, if he ever did drugs behind my back we would have a serious problem, I would lose all trust -and that is exactly what happened today, today I found out they did shrooms yesterday, although I don't approve of the drug use, I am more angry about the lying/hiding of the behavior

(Been together 4 years)

Would love some advice on what to do? What to say? I'm bad at tough love and I have never given ultamatiums before, but I'm open to it