He kept saying that I should be supporting him through this mental health crisis like he did for me
Well doesn't he sound charming as fuck. OP I have been in your spot, 18 years together when I discovered he was using escorts for about 5 years, he blamed my depression, he also blamed the fact that I had been sexually abused as a child, he used things that he knew I was sensitive and vulnerable about to hurt me all over again, they are all like this, blame, blame, blame, never their own decision that lead them to do this.
The sick feeling in your stomach fades, the heartache fades, for a time it will feel like you are grieving a death, you will be filled by self doubt as you question what is right, question your own intellect because if you were "wrong" about this person you loved and trusted what else are you wrong about? All those thoughts are normal.
My best advice is to speak to a therapist that specialises in infidelity due to use of sex workers/porn/sexual addictive behaviours (I am in Ireland if you need to pm me for the name of one) try to get exercise, I found walking greatly helped me, I also found mindfulness useful when it felt like my emotions were out of my own control, "Intimate Deception: Healing the Wounds of Sexual Betrayal" by Dr. Sheri Keffer helped some too. Her blog is excellent drsherikeffer.co/blog/
Legal and financial advice are a must, as is a health check ASAP.
If there is anything I can help you with please pm me, take care 