How could I have been so stupid:( what should I do? ?

He does have the right to be mad. But its not your falut that you thought you had something. there has been times where i thought i had something but it was nothing. you should always find out forsure if you got something before telling the guy cause if you do have something and they get tested and its neg for them they will know you were probly sleeping around. i would just give it time. he needs time to cool off and he might talk to you again or might not. If he wants to not forgive you then you just need to move on and forget him. he wasnt the one for you. Just make sure you give him space tho, dont talk to him, dont text, dont do anything that involves talking to him. if he has true feeling for you he will come back. I hope everything works out for you tho!