Oh gosh kudos to you for wanting to help/find help/find a remedy for this.
Not everyone could handle that enormity.
Just keep in mind that it will be a lifelong journey/problem/experience and daily.
And you too, along with he, would probably benefit from counseling, since there are so many issues to consider and even the most able human, always needs professional help to manage it, healthily.
He sees a Doctor for his meds... but is he also seeing a Therapist or Psychiatrist, since they are the one's who can prescribe meds as well?
You seem to be getting real affected by all of this, perhaps seek a support group or counselor for yourself... since you are getting depressed, and to get the right mix of meds for yourself.
Also, it is all something you really want to do/live with and "be" in your life? Or not? What are your honest feelings about it... and do you really want to do it or are able to? And if there are children involved... then how is that with respect to your/your fiance's emotional issues, and is the child able to cope, as well? If there are so many anger outbursts and fighting etc. then it must affect any child as well, in your family... and it affects you as an adult.
I would also consider helping or providing some sort of help for any child you have in your family, in dealing with this as well.... because children are always affected by these things too.