Advice

My fiancé, he's turning 18 I'm turning 17, is doing a favor for a close friend, who is in their mid twenties, of his. I have never personally met them but he's watching their kids for what was supposed to be 2 days. Well today is day number two and he is supposed to come home today. I haven't heard from him since he left. The last time he went to this friends house he came home drunk swearing he didn't do anything. Well I'm starting to worry and he's not answering anything. Should I be concerned?