I recommend just honoring your inner confusion and accepting it as a smart and normal way to feel. Your relationship was good in many ways, and you have a deep well of positive feelings around that. You mentioned his anger issues, which means he had some trouble with impulse control. Now you are aware that his impulse control problems produced a whole vast secret world within him you had no idea existed. In the mixing bowl of your emotions, that dumps in tons of shock, betrayal, fear, reassessment, suspicion, revulsion, pity, concern, all swirled together but not blended smooth.
So that's where you are.
Should empathy for him be part of the mix? Sure, but so should be a healthy dose of appropriate suspension of trust, and a concern for each of your sexual health. Get checked for all the sexually transmitted diseases. If that makes you feel ashamed or sullied, that is normal too, and is part of the complex reality you are in. Anger is appropriate, but don't let any of that delay you getting yourself checked physically for diseases.
In terms of the shocking details of his specific sexual behavior, he likes to "bottom" or submit really hard, it seems. It's certainly not unheard of for heterosexual men with this impulse to want to bottom to other men precisely because they hate it so much. Perhaps this is caused by his experience, but it is also just part of the way humans are, I think. The animal parts of our brain - the "lizard brain" - that control sexual action also control dominance and submission drives, and for some people all that seems to be wired together. There are thousands of men like him. Maybe there is an interaction between this bottoming urge and his personal biography, and his clinical depression, but I wouldn't get too wrapped up in all that.
I also suggest proceeding on the assumption that he may never change even if he wants to. It is also possible that he does change, or can minimize his acting out, but entirely possible he can't. It's the history of angry outbursts that suggests problems with impulse control. He also will not lose any of the wonderful qualities you love about him and about living with him.
So shock and confusion are actually appropriate responses right now. While that is going on for you mentally and emotionally, there are some pragmatic issues to address - getting checked for diseases, finding a local counsellor who can help you sort out all that confusion, finding a couples counsellor who can help the very difficult communication you and your husband will need to tackle together, and so on.
The bottoming urge is not only sexual, by the way. Some people can use it to become strong followers of a religion, or of a twelve step program, or some other thing they can submit to. That generally needs immersion in a supportive social context though - one where everything around you nudges you towards that form of self-subjugation. But not everyone can sublimate their impulses that way.
Complicated, isn't it?