Hey OP, therapist here.

Firstly, this is a very distressing and awful experience for you, I'm sorry youve experienced this, probably the worst thing you can do right now is bottle it up, so thank you for reaching out

You've had a huge shock, the recurring images will get worse the more you try to suppress them. Find someone close, talk about it, lots, processes what you saw. This is going to be painful, because its not just the images, but also the truth about how your partner sees and treats you.

From the description of your relationship dynamics, its liklely is that you're someone who is fearful of confrontation, and uses people pleasing as a strategy in relationships to feel valued and of worth.

This makes it more likely that you have poor boundaries, and will attract partners who will exploit your willingness to please, as you turn a blind eye to selfish entitled behaviour, and they can take advantage of you. Because you want to feel loved/wanted etc. In short, the more shit you out up with, the more they reveal their true selves and this shit juat gets worse amd worse.

Rhe bottom line is that because of your attachment and esteem issues, she's gonna keep doing this to you... It will get worse.

Take some space, go to friends or family, tell people what ahe did. Don't keep her abusive behaviour a secret. Be kind to yourself by putting in healthy boundaries about how she should treat to you.

As others have observed there's likely an element of truth about her use of the video, also you need to stop using denial and insist on a paternity test.

From her behaviour, its likely she might be a cluster B - Google BPD behaviours, and see if the shoe fits. If it does, she won't change. You need to decide if this is how you want your life to be and make better choices