I know there are STDS that can be passed through oral sex alone. Like herpes. Have you googled it?

I read somewhere that Chlamidia and Gonnorhoea can also be passed and contracted through oral sex, dwelling in the throat... I agree with googling it. Also, your can contract infections / diseases from someone who is already infected, even if there's only oral sex involved. he'd just end up with it on his penis / surrounding areas rather than his mouth / throat.

Speak with someone at a GUM / sexual health clinic and you can both find some answers about how else he could have contracted it.

don't assume he's cheated until you have proof.

thankyou both for your replies, i googled it and it says it can be transmitted through oral sex
thanks again x