OKAY. EVERYTHING FORWARD THIS IS TTLY NON-CANON IN THE ACTUAL SONIC UNIVERSE, BUT IF THAT WASN'T OBVIOUS, DERP.
After years of chasing Sonic, Amy entered a relationship with him. It didn't go well. After a strained relationship that lasted two weeks, Amy and Sonic broke up, both parties feeling bitter and resentful of the other. Amy attached herself to Shadow, in need of another warm body, and in need of comforting. Sonic however flung himself into the arms of Mina, who had recently broken up with Ash after he had cheated on Mina with Nicole(Who had recently gained a cyborg-esque body.). In an attempt to 'jealous' Sonic back to her arms, Amy dated Shadow for a short while, but eventually, Shadow broke it off for Amy's own good. In a last, desperate attempt to gain him back, Amy confronted him. Sonic snapped, and told her off harder than ever before. It finally got through to her. Months later, Amy had matured, and finally became what Sonic would've wanted, but she could never have him again.