Why wouldn't Gareth listen to reason?

Naomi Pemberton reluctantly agreed to a two-year separation from her fiance. Although she knew Gareth was the only man for her, he wanted her to be sure.

Then he returned, but by that time Naomi was caring for the illegitimate baby of her sister, Clare, and trying to help Clare's abandoned boyfriend cope with fatherhood.

Could anyone blame Gareth for jumping to conclusions and swearing he never wanted to see Naomi again?