i dont think trying to trick him in any way will help. you should just ask him why he came out negative when he should have it. either hes going to lie, and say it was just luck, or something;at which point you delve deeper. or he will admit to tyring to keep a secret.

another thing is, like Pookses said, is there anymore evidence of infedility? you cant go on an STD alone.

if he hasnt cheated, he could have gotten herpes from a former flame, then yall seriously did get lucky in that you only caught it after you had a child.

im not an expert on STD/STIs, but i do know that some, like herpes, can kind of lie dormant. idk whether a test would pick them up while theyre dormant, you should look into that. if thats the case, then again, it could very well be from one of your former lovers, or his, but not necessarily a current lover.

it just comes down to who caught it from who. is it possible you could have gotten from something non-sexual? like borrowing a friends bathing suit or something of that nature?

bottom line: you caught it from old flame, and it didnt get caught on tests until now.

he caught it from old flame, and you didnt get it until now.

he caught it from current partner, and is completely lying.

or you (or he) managed to catch it in a non sexual way (if this is the case, he might not be lying about being clean)

i think the best course of action would be to discuss these options (and any others you might think of) with a doctor together. he cant hide this from a professional, and you deserve the right to know. theres some privacy issues at work, but i think if you maybe talk to your doctor, he'll understand and allow you to sit in.

i hope i managed to help a little bit, im still new to this hehe. i hope everything works out the best it can.