Hello,
The initial light bulb moment can be both a relief and discouraging. Good thing about knowledge though is now you can learn about the disorder and make informed decisions on how to proceed. All the information can be overwhelming I know. Take it one step at a time.
It is also important to examine your own role in the relationship and that can be the toughest part of all. You have already done a good job in recognizing you may have some codependent traits. Most all of us who have been involved with a borderline are codependent to some degree. This isn't necessarily a bad thing, but when it becomes unhealthy it is time to make some changes.
Take the time to read the excellent articles and workshops available on this site and don't be afraid to ask questions. We are here to help you through this and lend a sympathetic ear when you need one.