I am sorry to learn of this situation.
Unfortunately this is not an easy matter to resolve. If you want to dissolve the partnership, you can force this through a dissolution action in superior court (this is not a very cost effective process, and you should try to first negotiate a resolution - also please see my short paragraph on mediation below - these matters are usually best resolved through mediation if you cannot reach a resolution directly).
If he has been taking money from the partnership, you can sue for breach of fiduciary duty, embezzlement, and breach of contract. Again, this can take time and money (I don't know whether this is something that has reached the point where you are prepared to undergo extensive litigation, but most cases should at least attempt negotiations or mediation first as litigation gets very costly. You can hire a lawyer to represent you in mediation - a lawyer will not give you any additional legal rights, but they can help you better leverage your rights and help level the negotiations field, this is especially true if you find yourself in a compromised or unequal bargaining position).
Short of filing a lawsuit, you can try to mediate the dispute with them - contact your local bar association and request referrals to mediators, a third party neutral can often help you reach a mutually agreeable resolution. Use the bar association's referrals to contact a mediator or two, the mediator will then contact the other party to set up a mediation session, and you can go from there - hopefully resulting in a formal or written settlement agreement, and save yourself the time and expense of litigation.