Sorry it's a long one.
Background: ExF and I were childhood sweethearts, together from 15 for about 4 years and engaged for half of that. We spent a lot of time with each others families including holidays, I was always treated well and felt included and loved by the whole family. ExF and I split (my decision) after he admitted to me that he'd got too close and had some sexual contact with one of his uni housemates. We were together for a few more months but I felt I couldn't trust him anymore. The split was particularly traumatic for both of us, he didn't want to move on and I felt due to it being my decison to split I was taking the blame - our families don't know the reason we split - I was young and embarrassed at the time and just didn't want it to come out, but by hiding the real reason of the split it meant I was seen as the bad guy.
I moved on and was with my now DH within a couple of months, ExF struggled with life for a while but I know he's now settled down with his own family. I haven't seen or spoken to him since a few months after our break up, this was over 15 years ago now. However, his brother (who I went to school with) lives next door to one of my family members and I occasionally chat to him when visiting my family. Our parents would also chat to each other if they ever crossed paths.
ExF's Mum had been ill over a number of years, going in and out of remission and I found out that she passed away last month (his brother told my family member). I'm torn on whether to send a message, I don't have an address for ExF, I could email, or send a card C/O his brother. I don't want to make things worse by dragging up the past when he's probably already feeling awful but I'd like him to know (if appropriate) that I appreciated how his Mum treated me, and that I care for how he must be feeling at the moment.
I just don't know what to do, it's been keeping me awake at night! AIBU (is it appropriate?) to send a message of sympathy or should I keep quiet?