Having a mental health disorder is very difficult not only for the sufferer but also their loved ones. Seeing someone you love feeling so low can be really tough.
Accept that sometimes you won't be able to help. And that's OK. Sometimes you will be the only person that can help your partner, and when you can't, chances are that nobody can. Some days are just so damn rubbish that no matter what anybody says or does it just won't budge. And that's OK too.
Don't take it personally. Sometimes I can be really irritable, snappy and grumpy and afterwards I feel really guilty for being so mean to my partner. It wasn't his fault, why did I take it out on him? Do not make them feel guilty. I'm not by any means saying that you should be your partner's punch bag whilst they feel bad but they will already be feeling guilty if they've been a bit short with you and it's not always his/her fault, as much as it's not yours.
Socialising can be hard work. Don't expect too much. Some days will be alright and your partner will be able to be around people and socialise, at least for a short time. Other times this will be a real challenge, especially for those suffering from anxiety disorders. I find that sometimes after a day's work it's almost as if I've socialised enough for one day and I can't take anymore without it feeling like a real effort. It can sometimes be difficult to tell which point your partner is at in this odd cycle so encourage him/her to be open with you and let you know what's going on inside, but remember that sometimes, we haven't a clue what's going on in our heads either. It's just as frustrating for us as it is for you.
Taking antidepressant medication is tough. This is something that I found particularly difficult and I know that my boyfriend found it hard to see me on antidepressants. Unfortunately my body didn't take too kindly to the medication I was given and it made me quite ill, resulting in me staying in bed for five days with severe nausea and no appetite. I would wake up multiple times in the night thinking that I needed to vomit and rushing to the toilet, and would wake up at around 4am every single morning usually unable to get back to sleep for quite a while. I survived on smoothies that week. This is something that's really difficult for both your partner and yourself - who wants to see their loved one like that? The good news is that this isn't what typically happens with antidepressant medication and my doctor said that I'd 'had a bad reaction', so don't expect this by any means but be aware that being on medication could be really difficult for your partner, particularly at first.
You're probably being more helpful than you think. Unless you're being totally insensitive and not at all supportive then you will be helping your partner just by being around. Again, remember that you don't always need to be having huge conversations or in fact talking at all, just your presence can be helpful. It helped me massively having my partner around and he became my rock throughout everything - offer your partner this kind of support. Watch a movie. Make them a cup of tea. Bring her flowers. Play his favourite video game.
Remember to take care of yourself, too. It can be very draining both emotionally and physically to have a partner with a mental health disorder. Whilst I encourage you to support your other half as much as possible you must remember to support yourself too. I cannot stress the importance of this enough.
They are still the same person they always have been. Don't lose sight of that person. It can be hard for us to remember who we are when possessed by mental illness, particularly as some disorders can cause behaviour that may be out of character. All the time that you still see your partner as the person that you fell in love with, you will help them to see themselves that way too. Remember why you fell in love with that person and remind yourself regularly, as well as them.