Combustion by Julie L. Spencer

Kaelen is the perfect boyfriend. Smart, athletic, attentive, and willing to keep their secret.
Abigail is the only girl at his high school smarter than him. With his 165 IQ, he can talk to her about anything; science, math, social issues… chemistry.
He just can’t date her.
Until the day he gives up trying to pretend he isn’t in love and the chemical equation that burns between them gets too hot to ignore.
Kaelen learns the hard way what happens when you play with fire, and Abigail pays the price. But she isn’t the only victim that night. Devastated that he hurt the girl he loves, Kaelen pleads guilty and faces the punishment he feels he deserves.
Five years and one prison sentence later, Kaelen and Abigail can’t ignore the evidence of that one tragic night, and they can’t ignore the fire that still threatens all their plans for a future together.

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