I think that it's possible but much more difficult. I think the best two options to go about seeking a partner if you have a mental illness is to either be open about it before you start dating or seek somebody that has a mental illness as well.

Also, I think learning and adapting to triggers, changes in mood, needs, or finding a balance especially when things become draining for the partner are paramount for a successful relationship when it comes to those with mental illness.

Personally, I refuse to let anybody who isn't either accepting and knowledgeable about mental illnesses or who has one themselves anywhere near my inner circle of friends let alone in a relationship with me. I also carefully screen potential friends or partners by examining their personality, how open minded they are, and how they feel about people or mental illness and if they don't pass my trials with flying colors, they get kicked out of my life.