I waited until my son was completely ready (he was 3) and he potty learned in a few days. He's had very few accidents (and his accidents were always related to overalls or playing at a birthday party and not going in time) - I could count on one hand how many accidents he's had in 1 year. He's fully potty learned, too, and has always used the potty for both pee and poo. Again, though, I waited until he showed me all the signs of being ready.
Your son doesn't sound ready at all to me - he tells you he dosn't want to be a "big boy". It sounds like your first potty trained easily, but by their ages it seems as though # 2 hadn't been born yet. # 2 is only 2.5 (which is still young) AND he has a baby brother. That can affect him wanting to do it.
Potty learning is about more than just an age and physical readiness. It's about emotional readiness, too. He doesn't sound emotionally ready to do it if he's telling you he does NOT want to do it.
Many experts believe that children aren't physically AND emotionally ready till age three. ALso remember, despite your experience with your first son, that boys are often potty learned after girls. Three really is an ideal age where they really understand things. My daughter started showing interest at 18 months, but I knew she wasn't really ready. She's 2 and I'm in no hurry to push it along because i don't want a bunch of regressions if she wasn't truly ready.
Maybe give it a couple of months and see if he's ready again. When you do, you must remain consistent (as you've seen!). But I would really wait if I were you. Then you could give him lots of naked time for training purposes, and remind him every 15 minutes. Don't use paper pull ups (glorified diapers). We are cloth diaper users here, so I used cloth training pants, too. My son couldn't pull undies down well enough, but the Potty Scotty training undies he was able to do easily. They have a small bit of absorbing material in the middle to catch the beginning of accidents - enough to keep your floor dry, but still lets the child feel wet. Hope that helps!