I have been dating a guy for about 8 months. A little while ago he took a photo of my in my underwear without my consent. At the time I wasn't sure if he was taking a pic of me but then I saw it on his phone which confirmed my suspicions. I confronted him about it and he became extremely defensive and told me that he did no such thing and then said "what kind of sick creep do you think i am". Afterwards he said that both him and I both knew that he didn't take a photo and that if I didn't agree with him he would break up with me. Does his harsh reaction and his verbal threat about dumping further confirm that he is lying?

Well if you saw the picture on his phone it is obvious he is lying.
It would bother me that he would tell such a lie even when you have proof. It would also bother me that he would invade my privacy like that.
He would be my ex.

He sounds like an unstable Mable. I would've laughed and said I guess your phone has a mind of it's own or a ghost took a picture of me on your phone. I'd be donezo with this one. He'll end up manipulating you in the future or flipping the switch and deflecting his own actions onto you.

Or using the pictures as a form of blackmail. I say call his bluff dump him and he will most likely end up confessing. He seems to think he holds power over you, by the threat of ending the relationship. I say turn the tables on him