Friend in need is a friend in deed . Need some advise please. I need to know when it's enough in a relationship and when it's about giving each other even more space ?

Me '38M'..best friend is '34M'. Hii everyone, thank you for taking the time to resd this. Just feeling a bit down and I thought I would reach out for some advice. I am male '30M', married and over the years rhe number of friends I have reduced considerably. My friend male also '30M' married Is my best friend from uni, brothers in arm.. we have been close for years and helped each other through tough times and good ones - death of his mum.. my wedding etc etc Friend since uni says - early 20s Recently for sometime now, things have been different. whenever I call or message it takes ages/ days for him to respond. Last year my grandma passed away and when I told him, radio silence.. a few months later when I reach out again he said that he didn't want to reply cause he felt everyone was out to get him ,including me. I sort of let it be even though to was saddening.. Came to his home town and requested to meet him and to date he hasn't made an effort saying its too far.. even mid way doesn't seem to be ok Another tragedy happened in my life yesterday and after trying to reach him for ages he replied. Since then no response or pick ups of my calls . Finally a message saying that he is busy this weekend... And to date no check in or any other messages... Not sure if I am making sense but I guess the question is when is it time to walk away from a friendship or is friendship about tolerance and understanding. He is sort of one my last brother's... Thanks and apologies if it doesn't make sense 🙏❤️ When is it about being understanding and tolerating a friend and when is it about walking away? To be fair,both of us have to some degree of mental illness..