I'm sure others on here can give you sound advise. I just wanted to pop in and say I completely understand your frustration! Having to come home, or just getting up from the chair to see, urine on the floor or him lying in it would be hard. You gotta clean the floor/crate and then clean him. However, please take a deep breath. He's only 5 months old, still a baby and accidents are gonna happen. I don't know if he's peeing because he has anxiety that you're gone. Peeing in the house when your home because he drank too much water.... I don't know. Is his crate a bit small if he can pee in it and then lay in it as well?
Good Luck. You're doing everything right. Give yourself a break and prepare for more accidents. Its ok.
Edited to add:
You can keep him on a leash while in the house to help with accidents until he's a little older. This way he's never more than 6 feet from you and when he gets ready to squat you can pick him up and run him outside.