My heart goes out to all of you with Bipolar disorder and for those of you that are living with someone who suffers from it.
Unfortunately, there is nothing you can do to help him get treatment until he is ready. The fact is that you cannot force him to get help unless he presents a danger to his own safety, or to the lives of others. But there are some things you can do to support him and reduce the impact of his illness on the family until he is ready to seek treatment.
First of all, you should know that you are not alone and that it is very common for those with bipolar disorder to resist getting any type of help especially when he's in a manic state. One of the frustrating things about this illness is that it distorts a person's thinking to the point where they don't realize they need help.
Second, don't threaten to leave unless you are fully prepared to follow through with it. Otherwise it just becomes an empty threat. Leaving may or may not be the best option for you.
Third, find out everything you can about this illness. The only way to fight it is to arm yourself against it. Read everything you can about it. Use books, websites, discussion forums, whatever you can find. Find a support group either online or in person. Support groups are filled with people who have been there and can provide some understanding. They can also help with advice, suggestions, coping strategies, and sometimes it helps just to have someone to listen to you. If he sees how dedicated you are to helping him, it may persuade him to get help.
Finally, the time may come when you have to realize that you have done everything you can to help him. At some point, it will be impossible for you to continue to support him without his cooperation. Only you will know when the time is right for you to leave.
Feel free to PM me and I'll help however I can.
Resources I Suggest:
Bipolar Significant Others
http://www.bpso.org
Mood Disorders Society of Canada
http://www.mooddisorderscanada.ca/
Tips for Family members of those with bipolar who refuse to get help
http://bipolarworld.net/Family&SOS/getting_help.htm
Books:
Loving Someone with Bipolar Disorder: Understanding & Helping Your Partner
I Am Not Sick I Don't Need Help!: Helping the Severely Mentally Ill Seek Treatment