Sorry you are having to face this.
I have just returned from the uk where I have just spent the summer supporting my mum through her second fight with breast cancer.
I can tell you that the first chemo is the worst. It's the stepping into the unknown that makes it all the more difficult.
In turns of support just being there is the best you can do. Be a voice if your dp can't find his. I know my mum was grateful for me asking the questions she was too scared to ask.
Be prepared for a long wait, often oncology runs late for appointments which will heighten anxiety and stress levels, books, snacks, music...whatever gets you through pack in a bag.
My mum is having chemo weekly. After the third week we got into a routine, which I'm sure
You will recognize and work around.
For instance. Tues =chemo. We know she will be starving after so right after the hospital we take her to wherever she fancies to bulk her up...doesn't matter the last few times have been KFC
Wednesday, she feels ok so she does her food shop and errands.
Thursday and Friday are rest days, minimum visitors.
Saturday, slowly starts to feel better
Sunday. A day for her to do what she wants
Monday, doctors for pre chemo bloods and checks.
And repeat.
Like your dp my mum has lots of secondary problems which interfer with the chemo.
The first two weeks we spend about 30 hours in the hospital in various departments for various reasons. It was bloody draining, more so than the first chemo session.
Be prepared for the depressive moods. It took me quite by surprise to hear mum talking so negatively at one point 
I wish I had asked for help.
Which brings me to you...make use of any resources offered. Cancer effects us all and the very worse thing you could do is burden yourself and end up burning out.
I wish you all the best on this long, frustrating and emotional journey.
Here if you need to talk 