He commented on my stretch marks, im totally embarrassed?

I've just started a new relationship with this guy who I really like. He's 28 and I'm 22. After a month of seeing each other, we decided to have sex last Friday. Everything was fine and I felt comfortable with him. I went to his yesterday and we were getting intimate during the day time. I've recently lost quite a bit of weight, I've never been on the chubby side but I had a bad few months this year and I lost a stone and half. After he went down on me he said, "Aww look at your stretch marks," Well I went blood red and immediately ran to the bathroom. I stayed in there for like 5 mins cringing, he kept knocking and told me that I shouldn't feel bad but I can't help it. I never wanted him to see them. He has said he doesn't care and he still finds me beautiful but I just can't get over it. How do I move on from this?