Hi Deli, 

I can understand your frustration but please give your partner time. 
2 years may seem like a long time, but to lose a parent I feel it is no time at all. I'm currently in the midst of waiting for treatment for my terminally ill dad, and while I'm so blessed to still have him here, the thought of one day him being gone is devastating me. Panic attacks and breakdowns multiple times a day, and yet he is still here. I dread to think how I will react when he does pass away. 
 

Something to put it into perspective is, we know and love our parents all our lives. We never know or remember a time they weren't here. Whether you were close or not, you have always known them, and loved them. 
To then have to adjust to knowing they are no longer here, no longer a quick phone call away I can imagine is a lot to deal with. We look to our parents for guidance and support, unconditional and sometimes tough love. Whether you are 4 years old or 50 years old, your parent will love you to the end of the Earth more so than anyone else would (with the exceptions of abusive parents), and to face knowing that in a way that love has gone, it's devastating. I go to my dad for EVERYTHING, boy trouble, financial advice, a laugh, tough love, work issues. Knowing one day in the future I will have to go without all of this as well as just not having him in general is a lot to cope with. 
 

Please give your partner time and space to grieve, I can imagine they have came a long way from where they were after initially losing their mom? It's a slow process, some deal with grief faster than others. As long as they are looking after themselves and living their every day life, I can't see what the problem is. If that isn't the case and they are neglecting themselves then you need to contact a mental health expert, as it's possible they could be dealing with some form of clinical depression/PTSD after the loss of their mom. 
 

Sorry if I have came off as harsh, I don't know your situation. 
 

I hope your partner is okay,

Hannah x