Falling in love with someone who has a mental illness is not hard by any means.
They are still people, and their mental illness doesn't define them. While it may change the way they behave or think, it does not make them who they are; it's just a piece of them.
As someone who has struggled with mental illness (depression specifically) throughout their lifetime, I found my significant other having a hard time trying to deal with me some days. With mental illness, some days are better than others. You'll be feeling great, then something may happen to ruin your mood, or you wake up in a depressed state and can't shake it. You can also have days where you feel great, and life feels good.
Those are the best days.
On those not so great days, you may push away your significant other. You may want to be left alone, or you may be incredibly hard on yourself and lose motivation to do everything. Those days can be hard on your significant other, and they may feel hopeless. Those are the days you need your significant other the most, but it's hard for them as well. This may make you feel like a burden or make you wonder why they are a part of your life.
While you may feel that way, it isn't true.
The person you're with fell for you. Every part of you. They fell for your good and bad traits, and they accept your mental illness. They accept you whether you're having a rough day or a fantastic day. You are not a burden to them at all.
I, myself, have fallen for someone with mental illness, and I don't regret a single thing about it.
It wasn't difficult for me to fall for them either. In fact, I fell for them harder because of their mental illness. I connected with them instantly because I understood what they were going through and how they were feeling. It made me feel closer to them.
Being with someone with mental illness may be hard sometimes, but it does not define them; it is a part of them, and you should love them even more on their bad days.
It's what they need.