“Love isn’t about effort -- I pour my blood sweat and tears into becoming more of something, and you see someone who already has those qualities and leave me.”
There are two halves -- the fundamentals, and the room for growth. We determine what is fundamental to our needs and what we wish to see in a partner, and we've made a bad decision for ourselves when we pick someone who lacks those fundamental qualities.
Then there's the room for growth -- perhaps you've found a partner whose character is of a high quality, sure. But they leave their dirty socks all over the house. Or they're not mindful with their money. Or they raise their voice too often. Love is the effort it takes them to overcome those habits because they know that it would better themselves and make you happy.
If you find someone is spending blood, sweat, and tears to meet the qualities you deem fundamental though, you've either chosen some really shallow qualities and deemed them fundamentals, or your partner isn't the right fit for you. Maybe they need more time on their own, or maybe they need to find someone whose fundamental expectation of a person matches up with who they are.
If someone better looking walks by and your partner jumps ship, they're pretty shallow and not a good fit for you. If someone with character walks by and your partner jumps ship because you have none, you're probably not ready to be in a relationship yet, no matter how hard you were trying.