When a father, just diagnosed with depression, learns that his sweetheart has an even more debilitating mental illness, he must evaluate the relationship and learn the importance of their love.

Have started again here:

https://loglines.org/when-he-learns-that-his-partner-has-a-borderline-personality-disorder-a-depressed-guy-endeavours-to-fix-a-relationship-disrupted-by-a-cloud-of-mental-illness/

Have started again here:

https://loglineit.com/when-he-learns-that-his-partner-has-a-borderline-personality-disorder-a-depressed-guy-endeavours-to-fix-a-relationship-disrupted-by-a-cloud-of-mental-illness/

Good points raised above I wont repeat them but add the bellow.

Better to make the inciting incident a more significant event than that in the original logline. if you want to deal with mental illness then why not have the stakes character (sweetheart) try to commit suicide or do some other dangerous action that relates to her mental illness. This way you will clearly motivate the MC and explain she has a condition of sorts at the same time.

Hope this helps.