I've never gotten into a relationship desperately thinking I couldn't do any better, but I have been stuck in some relationships for that very reason. How did that end up, well let me see. I would start playing a mind game I call "I'd rather". You say things like "I rather be by myself than miserable". You'll know you're winning the game when you play it so much you start believing it. Than finally you walk away victorious winning the game and a higher self-esteem.