First of all, there’s many different mental illness and I don’t want to give some wrong ‘advices’ from a cruel lack of informations but I’ll just share what I know. Being with a mentally ill person is challenging, you’ll learn about yourself as much as you’ll learn about your partner. No matter how “ ill “ the person is, it’s important to remember that you’re not responsible for whatever is wrong with her/him and you can’t fix that person (mostly because that’s not your job here and also because most of the time, people can’t be fixed) – what you can do though is get as many informations as you can about your partner’s mental state. Document yourself, go to therapy with her/him if he/she’s being taken care of, be patient (always, as can be) and don’t be afraid to ask questions. Communication is important. The thing you need to remember is that, as a “mentally ill” person, it’s very hard to explain what you feel and how you see things, people won’t get it though they’ll try to understand, it’s impossible to feel exactly the same and see life as these people see it. You need to be a caring, understanding person 24/7 as your partner probably needs to be understood more than anything else, they don’t ask for support or help, they mostly want someone who understand they’re sick and won’t judge them for it. Whether it’s a panic attack or a serious medical state, all you need (and CAN) do is to care for that person and love them. Obviously you’ll have breakdown and feel helpless sometimes, you’re only human, but remember that it’s also okay to take care of yourself in the process. The more you’ll feel sane, the better your partner will be.
Don’t try and fix him/her, because you can’t. Don’t be ashamed if you feel like it’s too much to take in as you obviously didn’t sign up to be a therapist, as cruel as it sounds. Some people need professional help sometimes, and your role as a girlfriend/boyfriend is just to be strong and care for that person, love them and always be honest. Don’t lose yourself in the process. Communicate. Just be there as a partner and know where your boundaries are ♥