Bound By It (Xianwang)

"A-xian, thi...this is your....your fr...frie...friend ya?" Mr. Jiang asked with a mix of confusion and surprise. He already knew the answer but wanted to hear it from Wei Wuxian and not assume anything, at least for now.
Wei Wuxian released the breath he was holding, swallowed hard and closing his eyes preparing himself to face anything that would follow said loud enough to not repeat again "Meet Lan Wangji, my husband"

How did a 26-year-old doctor, Wei Wuxian, who just went to a medical camp for 2 weeks, come back home married to a complete stranger Lan Wangji, who seemed barely 21 ?