Why does my boyfriend never put me first in his priorities?

my boyfriend and I have been together almost 10 months. I'm 26 and he is 36. There have been many times in our relationship where he has stood me up/failed to come over for dinner when I've cooked etc and just generally promised he would do something and then has failed to and gone MIA for whole nights at a time and written a colorful apology the next day. For the first portion of the relationship I was carefree and just understood and I guess 'put up with it' because I love him. But during the pandemic we moved in together for 3 months so we could be together, he worked through the pandemic and I did not, I spent a lot of time on my own. Many times he would get stuck at work and go MIA as usual, miss dinner and come in late but he started to smell like booze and act strange on these occasions. To cut a long story short eventually I got sick of it and had my doubts and went through his stuff one evening and found a packet of cocaine which sure enough explained everything. I confronted him about it, for him to say it was his friends cocaine and not his and he had just had a 'bump' as if to say this was better than having a full on line of coke (honestly no difference in my eyes). Anyway since we have lived together I've explained to him those months of him treating me that way and getting drunk & coked up with his friends instead of coming home to me and having dinner with me have really affected me and made me not trust him because then I just think all those times he stood me up before he was just doing the same thing and suiting himself. Well since not living togerher and the coronavirus has eased he has had a promotion and I've supported him but still he gets 'stuck at work', breaks promises, stands me up and is awake early hours on Facebook. This week my uncle died and last night he stood me up to be with his friend who is a 43 year old man and needed his support. I'm just sick of never being put first and being treated like an idiot by the man I love.
Why does my boyfriend never put me first in his priorities?
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