If he's insecure, this could very well be the end of the relationship, sorry.
It's excessive, I get it, but he thought you were the one, and thought that you felt for him what he thought for you when you first met.
What you have just told him was that (even if there was no sex), that you were testing the water with 'many', weighed options, and then settled on him.
If he's insecure, which it sounds like he is, whatever you say won't make a difference. He'll assume you're just lying to cover up 'more', and it will eat away at him, bit by bit, as you've basically just ruined his image of you.
MN will tell you to leave, with phrases like "he's insecure, I'd bin him off because you don't want to live your life reassuring someone". Honestly, I think this is on you though... He had this fantasy of you being exclusive, sunshine and rainbows, and that fantasy is dashed now.