I think what @MatchaToad has written is very sound advice if you commit to the relationship and want to be a carer ongoing, for that person. I have been an emotional support carer/punching bag for 2 people and I have unintentionally one it to 1 person my ex partner.
At risk of being unhelpful to your cause, I got dumped for having unstable emotions and it took me 7 years to truly address the root cause of the problem which was/is my own unstable emotions and attacking the person who loved me at the time or otherwise 'being psycho' and it prompted me to address my issues and drastically improve my internal resiliance and emotional dependency and my behaviour, too. As I had learned from my mother that throwing tantrums is the way to get other people to take responsiblity for the situation and relieve myself of personal responsiblity/emotional stress/confrontation.
When I was in the caring role I felt fairly important to being crucial to the other persons life and I thought that love was tolerating their bad side while hoping to get a glimpse of their good side which would come out when they felt like it yet each person couldn't or wouldn't improve their behaviour and addiction issues so when I put up boundaries, they moved off to find other people to absorb their BS.
There is a lot of life at stake but I would have a good honest moment to yourself to consider:
Is your partner taking responsibility to heal/address the background issues?
Do they compensate in other ways to add value for your life?
Does caring role align with where you want and need to be in life?
Are you getting enough good days to offset the bad days?
As caring for a person is heavy duty and I still care for some people in my life now, but they have much stricter conditions for how much energy they can consume. I lost years of my life caring for people who DID NOT address/heal/improve their issues and they are still crying, shouting, attacking like toddlers whereas I have moved forward into a more satisfying life.
So in the aftermath of this yes you have tactics for caring for the person but you also need to have tactics for caring for yourself and that includes approaching the other person for them to address their personal control of emotions and behaviour so that they refrain from relationship abuse.
Life contains many, many stressful and challenging days so people need to value the good times and minimise the bad times. It is not normal for every day, every week, every month to be an emotional rollercoaster and PEACE is the most beautiful and constructive energy you can being into life, from there you can make informed choices about doing things to benefit yourself and the world around you, too.