Raise your hand if you've ever had someone cancel a date on you because they made better plans 🙋. For some people, a night out with the crew > a night out with you, and TBH, they need to get their priorities in order. However, for the Myers-Briggs personality types that prioritize their relationships, cancelled dates are simply not a thing. For those who put their relationships first, not even a violent case of food poisoning could make them flake out on plans with a partner. (Though if that's the case, you should probably tell them to stay home for both of your sakes.)
Unreliable SOs don't necessarily care less about you than someone who always keeps plans. It's hard to say no when all your friends are going on a ski trip the same weekend you're supposed to visit your SO's great aunt in the nursing home. But it's usually the case that the personality types who take their relationships the most seriously are also the ones who don't make plans with a partner lightly. Not sure what your personality type is? Take the test to find out. You might be one of the types who always prioritizes their partner over potentially better offers.