How to talk about skin picking to a skin picker?

This is a really difficult situation for sure. I can offer one point of view from the other side of the fence. I am a skin picker and my boyfriend was very bothered by it. For a long time he didn't say anything, but just kept trying to offer me solutions for my acne. Then at one point, he told me that he really had difficulty taking any next steps in our relationship because of my problem. I'll admit, I did not respond in a nice way to him at the time. I denied that it was a problem, I blamed it on the acne and just said 'It's not my fault I have acne, if you can't love me despite my appearance, then you don't really love me for me.' It was really harsh of me, but I was really hurt. However, this was one of the best things that ever happened to me. It forced me to confront my problem, one that I was often in denial about. I became desperate and started looking for any solution I could find, which eventually brought me to this website. I signed up for the therapy, and it has totally changed my life. It has helped me with my picking, it has helped with my relationship with my boyfriend and with my relationship with myself. It was amazingly helpful to me to be able to learn about this condition and see how many others are suffering from it too. I always had felt very ashamed of my picking, and there was a lot of guilt involved, but it was this never ending cycle. Having someone else point out to you a specific thing that you are ashamed of is really painful to hear (even though I picked in front of him, I was still ashamed. It's like I just wanted him to pretend it wasn't happening and to be ok with it. If he would have done this though, we both would still be in denial and our relationship wouldn't be where it is today). It was hard, really hard, but we are both better for it, and I am really very happy in hindsight that he was honest with me, because it helped me to be more honest with myself as well. It will take time, lots of time, and ups and downs and lots of patience, but it is worth it. My personal opinion is that if you want to stay in this relationship, you will have to address this issue.
Eventually, when I came to a point that I was able to hear him out, what he told me was that he cared for me so much that it hurt him to see me hurting myself. This was hard to accept, but this is one of the things he said to me that was helpful, because I could see that he really was trying to help me. I think it is really important to let the person know that you do accept them with all their flaws and issues, that you're not rejecting them as a person because of this. You just care about them so much that you want the best for the both of you, and you can't have that without being honest with each other. I think it is also important that the person knows that you will be there for them if they choose to work on this issue and get treatment. Let them know that you will learn about it with them and do whatever they need you to do to be supportive. Listen to what they have to say, hear from your boyfriend what his experience is, it could be similar to mine, but it could be different. There are a lot of common themes, but everyone has their own experience. It is really important to just listen.
Please do not ask him to 'just stop' that is probably the most unhelpful thing that you can do. Another thing that my boyfriend would do is to look at me with this painful expression on his face when he saw a spot that I picked and he looked so dejected to see it and he would not want to kiss me or look at me, this was really difficult because it really escalated the shameful and guilty feelings that I was already having. So, I would try to avoid that if you can.
One thing that was helpful was after we both had talked about it and came to a place of acceptance and were able to 'work on it' together. He was able to learn what some of my trigger situations were and would do things to offer extra support in those moments. For example, there was a certain person in my family who could trigger me when discussing certain topics that caused me stress and that person put a lot of pressure on me. I would often start picking unconsciously in these situations. My boyfriend would start holding my and when he could see these situations were beginning to arise. Not in a restraining way (that would not help) but in just a normal loving, hand holding way. Just like any couple might hold hands in public. If I needed to let go, he let me let go, but him taking my hand was like an extra boost of support. A silent way of saying 'I know this is hard and I'm here for you.'
It is really hard to stop all together, and I would not expect that to happen right away (it may or may not stop all together ever). But if he could start with acknowledging and then gradually reducing, that would be a big step.
I'm sorry this is so long, but I hope it is helpful. I think the more you can educate yourself about the condition, the more you will be able to help him and yourself (and it looks like you are already doing that, so good for you!). Also, this is just my experience and everyone will be different, so listening without judgement is really important. Good luck, I hope for the best for both of you! Please feel free to ask any other questions, I am no expert but I am happy to share my experience if it will help someone else.