The more I think about it the more examples I come up with from over the years of inappropriate comments or touches.
You need to draft up this list now as you will then be able to see the patterns of behaviour and the totality of his abuse will become crystal clear.
All of those individual incidents / moments when your gut was telling you something but you felt confused in your head were all real proactive incidents of abuse in plain sight.
You need to know that you are 100% right - in what happened that day, in what happened in the past, in how you felt and how you feel about your DH reaction. You are 100% right.
You need to know that your DH is behaving badly and that this could be due to him also being a victim of his DFs manipulative, hidden, smoke and mirrors abuse and toxic control over the years. This might EXPLAIN his reaction to you right now - but it doesn’t EXCUSE it in the short term.
You could be generous, for now, if you believe your DH to be at his core a kind, respectful, honest, loyal man, and look at his actions as him going through the numerous stages of grief as he has had his family narrative obliterated.
Hopefully he is in the very first stages of grief - shock and denial - if so he will then move on to anger (with his DF), then depression and then acceptance. He might go back and forth between the stages. He might get “stuck” at denial. He might well need outside objective professional help to pull him though this. No idea how long this could take or even if he will progress through.
None of this is helpful to you tho. He is either psychologically unable to help you right now or unwilling to help you right now. Only you in time will know which place he is at and where your tolerance and boundaries lie.
In the interim I would look after yourself and set your own firm and clear boundaries - I would not look to him for support, approval or validation but would make sure I sought the support I needed elsewhere rather than wait for him to see the light.
It is also not for you the victim to spend your finite emotional energy drained trying to get him to see the light. You need to conserve it for healing yourself and riding the emotional roller coaster which will now hit your family which ever way your DH decides to jump.
You were sexually assaulted on that afternoon - and for years before that you have been abused, groomed, tormented and manipulated. The darkest thoughts that you had about him were and are true.
Know that.
Don’t let anyone gaslight you anymore. This is a #Me Too in your family. How did your DH behave when you mentioned “confusing” incidents to him before - did he minimise them?
What boundaries and next steps do you want to put in place with your FIL right now?