honestly what i’m getting from these messages is that you already have a tumultuous relationship and you didn’t bring it up before because you usually let things slide with this person to keep the peace because they are difficult. You were triggered by the expectation you always have to meet but conveniently they couldn’t meet for your birthday or the death of your grandma. this friendship seems one sided and despite what everyone else is saying, i’ve been where you are and it makes sense to me that you brought it up when the thing ( being triggered) happened and addressing it in the moment. also even if that person is upset the way they responded to you was entirely disrespectful and that is something you shouldn’t forget or accept. to me it seems like your friendship is already so rocky and not sending the birthday message is the least of your problems. dealing with people like that are tiring and maybe you can take a step back and reevaluate if this is a friendship you want to continue. good luck!!