Why does he keep sending me pictures of himself?

A selfie on its own tells you very little. The pattern around it tells you more. Look at whether the pictures come with a question, a comment about your life, or a plan, or whether they arrive alone with nothing attached. Photos that come right after you've said something personal, or during a stretch where you were both actively talking, usually mean he's trying to keep the thread warm and wants a response. Photos that show up after a long gap, or while he's been short and distracted on everything else, often mean he's reaching for something easy to send.

Also look at what the pictures show. Shots in different places, with friends, or doing something he likes tell you he's showing you his life. Repeated near-identical mirror or car selfies, with nothing changing but the angle, usually mean he's fishing for a reaction to his appearance and isn't inviting you into anything. Neither reading is certain, but noticing the difference lets you respond to what's actually there.

Two kinds of reply tend to work. The first is a light acknowledgement that stays on the photo for one line and then turns outward, like a comment on where it was taken or what he was up to. That shows you noticed him without making his appearance the whole conversation. The second gives him a real question about what the picture means to him, like what he was doing or what he's looking forward to this week. That second kind asks him to talk, and talking is what you need in order to see whether he's interested in you or only in being looked at.

You can tell a draft is working if it has one thing about the photo and one thing about him. It isn't working if it's only praise, only an emoji, or only a request for more pictures. Skip any hint that you're keeping count of how often he sends them, and skip any joke that makes the photos a running gag between you.

Send your reply in the evening, or the next time you'd normally talk. Don't fire it off in the middle of a work block or at two in the morning when you're overthinking it. If he answers with words and a question, keep going. If he answers with another photo and nothing else, reply once with a conversational line and then wait. If he goes two or three days without asking you anything back, don't chase him with a fresh picture of yourself or a clever opener. Let the gap do the work.

If he keeps sending photos and never engages with what you say, that's your answer. Stop replying to the pictures and say something plain, like you'd rather talk than trade photos, or just stop responding to that thread. You don't need to explain why you're stepping back. You're allowed to end it when the conversation only ever goes one direction.