Your instincts are right — to make an appointment with a therapist. If you need help locating one in your area you can check the find help tab at the top of this page.
There are three things that are bothersome about this situation and it makes sense that you would be very upset and disturbed by what happened. First, he asked and you said ‘NO.’ This is important because it was clear that you did not want to do this, and he was specifically told this by you directly. There is no doubt or confusion.
Secondly, you were undressed after you told him ‘NO.’ This means that there was never a ‘yes’ given. Your boyfriend took your lack of response as a yes — this isn’t okay.
Finally, the light is being interpreted by you being videoed without your consent, which is leading to you not trusting him, feeling traumatized, and turned off. All of these things can have a direct result on your mental well-being and a discussion with an experienced therapist in PTSD would be very advisable. I would make this appointment sooner rather than later because this isn’t just about your relationship with your boyfriend, it is about how you will feel about other relationships in the future.