My last relationship taught me that the more chances you give someone, the less they value you.
They're not afraid to lose you because they know no matter what, you won't walk away. Never let someone get too comfortable with disrespecting you.
Be careful with this idea that everyone is replaceable, there are Some people who come into your life and you won't meet twice in life. Some people are special by nature and their presence in your life made things better and you know it.
Make inconsistency your number one dealbreaker and watch your love life improve. They can't communicate, be considerate of your time/feelings or make the effort to make you a priority? Fine. Life's too short to spend waiting on people or wondering if/when you'll hear from them.