A.F.
M.-
I'm sure your 3 year old feels slightly embarassed and frustrated but you're doing the right thing by keeping your cool. Trust me, he doesn't want to sit in dirtied clothes any more than you want to clean them.
I went through the exact same experience 10 months ago with my oldest when I had a new baby. My daughter had been trained without any accidents for nearly a year. With all the changes in our house after I brought her brother home, sometimes she'd make it to the potty and sometimes she'd have an accident. This lasted ~3 weeks and every time we reassured her that it was no big deal and happens to everyone at some point.
If your son was completely potty trained before, I really don't think the accidents will last. Right now, I'm sure he's confused and wants nothing more than to still be the only light of your life. Give him as much positive attention as possible and reassure him that you love him no matter what!
Stay strong!!! :)