You've been dating this person for 18 months, yet you don't see each other regularly at the weekend, because he's 'busy'! What you're effectively saying is 'my boyfriend prioritises other people/activities at a weekend, so fits me in when it suits him'!!
You both made plans to spend the weekend together, because you haven't since July! Instead he's decided he's going to meet friends and participate in his hobby.
Honestly, given that he's behaved like this before and you've spoken to him about it, and nothing has changed...end the relationship. Your boyfriend isn't interested in a serious relationship with you, his priorities are himself, friends and his hobby. He's happy to see you, when it suits him, but outside that, you aren't a priority to him.
Leaving in the early hours of the morning without telling him or at least having a conversation, wasn't the best way to handle the situation. I hope you have at least told him that you're at home and safe.
You need to think about what you want from a relationship and if this relationship is giving you what you need. In my opinion, it isn't. You both are viewing the relationship differently and so are your priorities. There's nothing wrong in that at all, you're just incompatible.