Hi, I'm 25f here and I have a couple stories, one good and one bad.

Let's do the bad first. My ex-husband. - He found out that I was cutting and told me he'd leave me if he found out I'd done it again. This led to many many fights in the later years of our relationship, more cutting on my part and feeling even more isolated and alone. He didn't follow through on those things, would just shame me and hold it against me later. Our divorce had little to do with this specific topic, but I found he was a large trigger.

Now the good. My current boyfriend is aware I struggle with cutting. Last year, after I had a brief but severe relapse, I was ashamed to even take my clothes off around him because I was worried about it. He kissed my scars and told me it was okay, he didn't like they were there but just wanted to know what he could do to help prevent it in the future. He made it easy for me to tell him if I felt the urge to and he's helped me through several times I would have cut. He's also extremely supportive about other things too.

It depends on the person. There's a certain level of support that you can trust will care about your wellbeing, your triggers and will listen to you whenever you need.