The guy I’m (f27) talking to (m29) sent me an unsolicited picture of his boner, I’m not ready for anything sexual but I still like him and want to keep seeing him. How do I respond?

So I’m just getting back into the dating world after going through a really toxic breakup and have been very picky on who I’m giving attention to. There’s this one guy who I’ve known since I was in high school. He was always so sweet to me, even when I was 50 pounds heavier years ago he still wanted me then too. We went out on a date right before my ex and I got together about 2 years ago. It was really well, he was a complete gentleman and extremely respectful. I didn’t end up seeing him again because that was right before I got with my ex. Anyways fast forward to last weekend, I decided to give it another shot. He took me out on another date and again he was such a sweet gentleman to me. Our conversations are really nice and have never once gotten sexual, except for one time when we were talking about cooking and he said to me “I think you’ll be my favourite meal,” I guess he means going down on me? I just ignored it and changed the subject lol. We were texting today, he told me he just got back from the gym and sent me a mirror picture with him in his boxers and he fully had an obvious boner. I don’t know how to respond, I like him and I want to keep talking to him but I’m totally not comfortable with anything sexual until I spend more time with him and have a more clear idea of where this is going. At the same time, I don’t want to say something that will make the situation awkward or uncomfortable. How do I reply in a way thats setting my boundaries while also making it clear that I still want to see him/not make it awkward?