Advice for raising a difficult toddler

Hey dads,

I'm looking for some advice for working with my 5-year-old boy. He's an amazing kid, and an awesome friend to his two younger sisters (3yrs and 5mths). He's smart, and loves to socialize. He gets discouraged quite easily when doing new things, so it takes a lot of patience and persistence to teach him things, which generally doesn't bother me too much. It's forced me to get creative, and there's an element of sanctification involved in here (for the Christian dads out there).

However, he has a really hard time taking no for an answer, and his temperament is super unpredictable. In most cases, instead of asking for something simple he defaults to melting down. Lately it's gotten worse, and it's really been taxing. Most interactions have become semi-unpredictable, and it's lead to us being significantly less adventurous with our time and, in some cases, less generous towards him.

I liked to think that he was just going through a phase, but this phase has been going on for years, and his school has admitted that his behaviour isn't really age-appropriate anymore. I overheard his classmates making a remark about his behaviour, and that crushed me.

People tell me to "enjoy these moments", that they "go past quickly". But the same people actually just didn't have a kid like this. I love my boy, and I just want a sane, manageable relationship with him.