Did your couples therapist talk about it at all? I told my H about self-harm a few weeks ago on a Friday (it had happened the previous Sunday), then we saw our marriage counselor the following Monday (he'd had to cancel the week before unfortunately), and he helped put it in perspective. Like he talked about the reasons why some people do it (can distract you from emotional pain and/or self-punishment--mine was the latter), that it's not the same as wanting to end your life, etc. If your therapist didn't talk about it much, maybe see if he /she can the next session. Or call/e-mail/text him/her, if you're allowed between-session contact, and ask for advice on handling it with your partner.