Making someone "see the problem" is missing the point entirely. Firstly because often, people with depression are fully aware of how they are treating people. They simply can't help it.
Your role as a partner is to love and support them. You also, however, need to prioritize your own mental health and happiness. There is an extremely common relationship 'trap,' one I've lived through. You are in a relationship that is causing you personal distress and unhappiness -- but your love of the other person makes you feel trapped. You can see how much they are struggling, and can't bear to hurt them -- often because you are afraid of what may happen if you leave.
When you love someone with a debilitating illness, mental or otherwise, you need to decide whether you can accept the other person as they are. If you can, then you have to do that, and choose to stay with the person precisely as they are -- while having and enforcing healthy boundaries. If you cannot -- and often times there are extremely good and valid reasons why you cannot -- then you owe it to both of you to discuss this and potentially end the relationship. Sometimes such a conversation can be the spark of change for the other person, but often times it isn't, and that's okay. Staying in a relationship that is making you miserable is doing no one any benefit.
It's a supreme challenge with depression, but you cannot allow the depression your partner experiences to affect your own emotional health. The best tool for this is something called "loving detachment." I'd recommend you read about it, and about the concept of co-dependency in general(*). It was a life saver for me.
The worst relationship mistake you can make (after the obvious choices like affairs or so on) is being in a relationship with a mirage. Too many people have a false ideal of their partner -- their partner after they've been "cured" or "fixed" or "realized the problem" or "got clean" or whatever. You cannot have "you must change" as a condition of the relationship. Either the person will change or they won't, but staying in a relationship where you expect the other person will change is controlling and damaging. Are you in love with the person? Or with a made-up vision of the person you have in your head? Remember that love is unconditional.
The best thing I did in my relationship was spend a year (I'm not exaggerating) thinking about the realities of the situation, the options I had, the way my life could end up whether I stayed or leaved, and so on. It was an extremely difficult time and required the help of therapists, both personally and as a couple. In order to do this properly you need to admit divorce as a possible end -- and I don't mean the empty threats of divorce many of us make. For instance, the hardest session I ever had was when my personal therapist pushed me to walk through a concrete plan for leaving. Where would I go? Who would I tell? How would we split up our possessions? And so on. Making the possibility real is extremely important. In order to not feel trapped, you need to fully believe that leaving is an option.
In the end, the decision I made for myself was that I could accept my wife as she was. Almost immediately my mental wellbeing improved drastically. I no longer felt trapped. My wife's depression did not magically become cured, but I learned how to detach from it and be a good partner while protecting my own health.
In the years since, my improved wellbeing and happiness has slowly but surely helped turn the relationship around. Her depression is still not cured, but now I know how to be a good partner for her, which has in fact helped her to a large degree. She now trusts me as someone she can turn to for help, rather than viewing me as someone who was taking her mental health personally (which I was definitely doing). In the end, this is thing most spouses don't want to realize -- it's you that has to change, not your partner with depression, whether that means leaving the relationship because it can't and won't work, or learning to love them as they are.
(*) It can be really easy for spouses to take suggestions like this personally. I know I did. Being called co-dependent by the couples therapist felt like a full scale assault. How dare he say that I'M the one with a problem!! Doesn't he know what I've BEEN through?? What I was missing is that he was telling me that to help me. Learning about co-dependency -- and how to overcome it -- was the most liberating thing I've ever felt.
