my son is 3.5 yrs-old...and is just about what I'd call fully potty trained...but that doesn't mean we didn't have our back 'n forth moments! I'd say that you should relax on potty training for a little while. Let him go back to diapers or use pull-ups. You haven't mentioned if he will do #2 in the potty or not. If not, then put him back in diapers, cuz pull-ups do NOT handle #2's! Give him a week or two or relaxing on the subject of potty usage and see if he brings it up. Keep the potty out in sight for him to use just in case. You can throw some reminder comments out every now & then ("wow - this potty just sits here & no one uses it...it must be lonely") =) Then...after a break, start training again - see if he'll keep a pull-up on instead of a diaper...see if when you ask him to go potty, will he go? Let him sit on the potty with clothes on for a few with a book he likes. If you don't have one already - get him a potty book or workbook that has either characters or a storyllne he can relate to. My son has a great potty book called "It's Pottytime" (Smart Kids Publishing - www.pentonoverseas.com) and it's for boys ...he also had an Elmo/Sesame Street workbook called Potty Book Coloring & Activities (Bendon Publishing - www.bendonpub.com) - he still reads the book sometimes when he's on the "big" potty and he reads/colors in the workbook when we're on the road in the car.
It's a long road...sometimes longer with male children...but it'll all work out in time. Although I know it's tough, don't get discouraged. As someone once told me - unless there's another underlying physical or mental problem - most grown men know how to use the bathroom!
good luck!