I'm dealing with depression and my boyfriend is bi polar. How do we handle this together?

Don't even try. You need to be supportive of one another, but you are individuals with individual problems. You are not likely to be ready to improve at the same time, nor to respond at the same rate. Tying your improvement to his, or vice versa, compromises both. Each must get strong/well for the relationship to be healthy. But when the 1st one improves, the other has a better chance. Just get started on yourself.
Big challenge. Mood symptoms can cause a lot of stress to the patient and his family. If u really care about each other and want this relation to work ; 1- u both have to be compliance with u medication 2- to refrain from illicit drug use 3-have family therapy and individual therapy 4- be supportive of each other5- make time together to enjoy u hobbies and enjoy each other company.
Ask for help. Ask for help from your doctor or see a psychiatrist will be a good start.