You've not mentioned 'love', so by virtue of your omission, I'm guessing that you're not in love with your partner anymore?
Of course everyone has the right to be happy, but I think to ask such a vague & ambiguous question, is in fact entirely unfair - and to put all the blame on your partner's MH issues is very easy & convenient!
I have MH issues, and my relationship is coming to an end... and I don't know why, I really don't (and thinking like this makes me cry).
I have bipolar, and my DH blames all of our problems on that, and he could easily post on here, saying "my wife has bipolar & I can't take it anymore", and I imagine the posts sympathising with him would be many.
It doesn't take into account that in a relationship both parties have a duty of care & responsibility to each other. I'm not saying that anyone is responsible for another's happiness - that is ridiculous, bound to fail, and just inspires a 'needy, dependent' relationship! But if one person has MH issues, then the other partner has a duty not to inflame the situation & worsen the MH of the other.
For instance my DH went on holiday (alone) when I was heavily pregnant (to a nudist beach), then again when DD was 5 months old. I had severe anxiety when he went for the second time, and it triggered a worsening of my symptoms, to such an extent that it took months to recover from. Most (sane) women would have a problem with DH going at such a time, let alone someone 'vulnerable', but he did, and he blamed the subsequent distress on my illness.
He also has done other 'questionable' things (photos etc), that other women would struggle with, but again it's my illness that's at fault.
I'm heavily pregnant at the moment, and tired because of this, and looking after a baby too, and feel... bleurgh! I used to go to bed at 9pm, but have made the effort to stay up late, because he wants me to. But he never comes to bed early with me, he always has to have 'another' cigarette, and by the time he comes up - I'm shattered.... I yearn for him to show me some passion, some desire... we've talked it over countless times, but he's just not interested in mt. Therefore I've not shown him as much affection, as I can't bear to be rejected night after night. As a result he's now not talking to me (and hasn't for 2 days), and I know that he's going to end it, my illness will be to blame - again!
So is it OK to leave a partner with MH issues? It depends on whether it's really that, or whether there's an underlying problem.
And if they haven't changed since you met/married them then it begs the question - why on earth did you marry them???? If it was in the hope they changed, then it is you at fault, as they've not deceived you in any way!