"Love Island USA" production member James Barker died suddenly last week while the reality dating series was filming in Fiji ... leaving his partner completely devastated. Adam Roth tells TMZ ... "James was the absolute light and love of my life. He brought joy and brilliance to everything he touched." James' partner adds ... "His loss is unimaginable. While it was not enough, I am so thankful for the time we had and the memories we made together." He noted the couple met at a Billie Eilish