Some context upfront: DM is in her early 60s and has stage 4 cancer which is treatable but not curable. Oncologist has indicated that, with treatment, she could still be with us for many years.
DM has been in a 'relationship' (for want of a better word) with a man she used to go out with when she was a teenager before she married DF (who died during the pandemic).
I was initially (cautiously) happy for her, as I knew how lonely she had been since being widowed. I've never met this man but DSis has and said he was OK.
However, he then broke up with DM the day before her birthday. DM messaged me and all my siblings saying how upset she was and what an awful person he was to do this to her - we all sympathised, and tried to make sure she still had a nice birthday.
She then got back together with him, and this then became a cycle where every few weeks or so there'd be a distraught message saying it was 'definitely over this time' - only for them to be back together within a few days.
Her most recent visit here (for my baby's first birthday), she spent most of her time texting him and essentially ignoring us.
It's got to the point where I can tell that he must have broken up with her again because she'll actually get in touch with me, rather than waiting for me to contact her.
A few weeks ago, I was going through a particularly challenging spell with my mental health and she sent another one of her 'it's definitely over this time' messages and asked if we could have a call so we could talk about it as she was feeling so upset. I replied saying that I didn't feel comfortable talking about her boyfriend and was it something she could maybe speak to a friend about instead.
She replied asking 'is it about DF?' but said I didn't have to answer if I didn't want to (so I didn't).
She has since been saying (in vague terms) that she isn't coping and is very down.
AIBU to not want to talk about this?
I veer between feeling like I shouldn't have to be her unofficial therapist and feeling like she has had this awful diagnosis so I should just be doing everything I can to support her emotionally.