Boyfriend and "processing"

My boyfriend is amazing. I love him and we are great together. Planning to get married this year. All good. The issue is that every once in a while, his family (sister, mother, son, ex-wife) will act out in a way that makes him upset. Then he goes into “processing mode” and becomes distant and neglectful of our relationship. This weekend, he didn’t respond warmly to all the anniversary celebration texts and notes I sent him all day. I knew what was happening and did thought work to keep myself loving him and enjoying the day on my own. It worked until bed time and he still hadn’t called and then I became upset. I gave myself kudos for holding out as long as I did, but I’m sure this will happen again and I would like to make it a non-issue for myself when it happens even if it’s on a special day. Help!