It's a difficult one I think. I need to probably get some feedback from DH and then pass it onto you.
The most important thing is to agree a care plan with his psychiatrist. Included in that would be what to do when he starts to crash again, numbers to call and how to get him into specialist care before he goes too far the other way. Crisis line, community assistance etc for his crisis action plan. Part of the wider care package.
But much of it is really your DP's responsibility to ensure that he's got these strategies in place to stop the illness from escalating. You can talk to someone who's in a manic phase till you are blue in the face and they won't acknowledge what you're saying. This is why the support of your community mental health team is so important as they are the professionals who move in to take over.
DH would also say that continual communication between the two of us is so important. He 'talks me down' for want of a better expression quite often and puts me back to somewhere more rational then we go and see my psychiatrist.
There is only so much he can do. He's had to follow me surreptitiously in the car/walked behind me when I've taken off in the middle of the night to keep an eye on me, for example. Or when I have been suicidal he actually quit a job to stay home with me. It's not sustainable unless the person with bipolar gets treatment and sticks to the plan. I rant and rave about it sometimes but you get over it and get on with it otherwise life is unbearable for everyone around you.
If your DH is refusing medication or refusing to seek help I really don't know what you can do short of contact his GP or psychiatrist for intervention and assistance. You aren't trained to deal with this, all you can do is try to get him to the doctor and enact your crisis action plan. And let them take over.
He's got to want to help himself. And you've got to have some support too - I'd recommend visiting www.bipolaruk.org.uk/ who have carer support forums and information for carers as a good place to start. You don't have to go it alone 