I don’t think you have anything to apologise for. What you did is react to your partner, who has previously had addiction issues, going out and doing cocaine. Why wouldn’t you fear the worst? Why wouldn’t you think he might be over-doing it like he’s done before?
If he’s previously had addiction issues he can slip back into that easily. Why does he think he can go out and do a couple of lines like it’s nothing, if you’ve been through the trauma of dealing with his addiction in the past and all the problems it likely caused?
I don’t trust my partner in the slightest at the moment given he’s just been through addiction and is in recovery. I don’t know how long your partner has been in recovery, but the trust isn’t something that comes back easily. If he announced tonight he was going for “just a couple of lines”, I would lose the plot. So I think you’re being awfully hard on yourself if you have previously stuck by an addict in his worst times x