Feeling stupid 😔

Long story short, started talking to this guy on a app and we got on really well but we go through these stages where I feel he's not interested in the conversation. On whatsapp for instance you can see if it's been read (a couple of times it has and he didn't reply until ages later). The thing is I think this is mainly because I have loads of insecurities. I've told him both that I'm insecure and that I feel he isn't interested: he said really reassuring things to me about my self esteem and that he is interested but I can't shake this feeling. Could it be my gut or my trust issues? I feel I want to stop talking to him but he has my number and I'm worried what he could do, even though he doesn't seem at all malicious but I'm just concerned 😕 also I do like talking to him but we go through these stages. Some days we have amazing funny chats but later that day it could be like we're strangers and I don't want to keep bringing it up with him. Help? Please don't comment that I'm too young because I'm 18 but I have issues listed the length of my arm 😔