Hi Paul Heather,
Thank you for submitting your question. It sounds like your partner has problem trusting others because of his past.
If he refuses to believe you, perhaps your friends can explain things to him. Another alternative is taking a home nicotine urine test to prove to him that you have not smoked. You should know that secondhand smoking can sometimes cause false positive results. However, there are test strips that actually show levels of nicotine and can distinguish between first hand and second hand smoking.
I hope this is helpful to you.
It is unfortunate that your partner refuses to believe your friends and your son. He certainly has issues with trusting others.
If you truly want to prove your innocence, a urine nicotine test may be the only option in this case.