M.K.
*hugs*
First of all you are not losing him at all. Think way back to when you were his age and all the mixed up hormones that made you so insecure, moody. Now I am not saying he should be rude but sometimes at least with teenagers you have to pick your battles, it he is moody maybe he needs to talk to talk to a therapist or ask him if he has ever popped into his counselor at school for a chat. Just keep opening up your lines of communication, get him help with school by either calling teachers or getting outside help. Do not just decide you are losing him. Working full time is not an excuse I am sorry if that sounds harsh but your kids out rank your job and your boss would understand if you needed to take off a little here and there to meet at school with teachers.
My daughter sounds just like your son minus the girlfriend or boyfriend for that matter. We are moving out of state and she really is effected by this.
I wish you lots of luck but really this is normal and they always come around. Just stop and think maybe he needs to be heard a little.