oh, OP. I'm so sorry. he's absolutely not telling you the truth, and they absolutely had sex. she mounted him at a work conference, he did nothing to stop her, but nothing sexual happened and they just drifted off to sleep in each other's arms twice? no one does that. that's not what happened.

your boyfriend has no respect for you or your relationship, and he's voilated your boundaries countless times. his assertion that he's unwilling to be with a woman who has already been married because of how steadfast his beliefs are in the sanctity of marriage is hypocritical and ridiculous.

I highly suggest you take good care of yourself. take a step back and focus on your own therapy, and what you think you deserve. I don't know you but you certainly don't deserve this.

this is your boyfriend's fault as much, if not more, as it is J's. if you're truly wary or afraid of her, make your profiles private and up security at your residence and workplace. you can easily find out what she's been arrested for.

also, her husband really deserves to know what's going on. you might want to head over to r/survivinginfidelity because I don't think your boyfriend understands the consequences of how his many, many intentional lies, cheating and disrespect have really had on you enough to be ready to reconcile.