This is going to sound extremely callous. And I would have thought so too before I had a son and before I saw parents handling things this way. I'm not sure how or if you have disciplined the whiny outbursts, but here is one style. It's not for everyone.
I saw it first before I had kids in my relatives on my mom's side. They have massive families from 5-12 home schooled kids each. My Step brother and his wife have 6 kids. His toddlers were never ALLOWED the dramatic outbursts. Hold the phone-don't call CPS everyone-he didn't squelch their emotions or crush their spirits, they are all happy vibrant older kids now, but "no pouty face" was always the rule with every toddler, and it was enforced firmly. No excessive whining over an injury or incident was allowed. After the normal comforting, that rule was enforced firmly if a child dragged it out. It simply wasn't allowed. It's a necessity in families that big, but even having only 3 kids, it's been invaluable for me.
When you go to their house and the kids are climbing on the rickety tree house they nailed up themselves unsupervised in the woods and someone falls off and gets a huge goose egg, they come in, nurse it themselves, and insist it's fine. I'll be freaking out like, "Woah, what did you do??!!" And they'll be like, "nothing". Even the girls. They were literally "programmed" to be tough form age 18 months. Even the most delicate ones at birth who were really whiny and over dramatic as toddlers. It was disciplined as a misbehavior unless it was a legitimate injury or sadness or anger thing, and even then, it had to be expressed appropriately with no excess fits. Sometimes when they're all together running wild doing hair raising things, there is literally no sympathy when the kids get hurt unless they broke something or are lying there bleeding. They don't even bother telling a parent. That's the extreme, but I notice lots of boys these days are super sensitive little time bombs at the park, and there should be a balance. I don't know how their moms deal with them at home, but at the park they seem to be coddling them and sympathizing with them a little too much even when they are being aggressive and mean to other kids because they're mad because they fell or something.
When my son was born he became super whiny and needy at around 18 months, and by 2 we had turned it around with that enforcement. He's now cheery and tough. Still over dramatic by nature and sensitive and sweet, but wont' milk it. He may start to whine at 3, but will stop at a warning.
Can you toughen up on him? I don't know what you use for discipline, but what are his firm consequences for acting so thin skinned? Have you implemented firm consequences the minute he starts to act out after one calm warning EVERY TIME? If not, this could help. If he's already obedient and kind, he should understand rules if you make it a rule that he doesn't act that way. Have a sit down, spell out the new program, and let him know what will happen if he lashes out at small things. Follow through immediately every time. This can work on older kids. My step sister was divorced and her sons 8 and 11 were really acting out. She moved back home and everyone pitched in on the discipline and they're super good now 2 years later.
Treat him with respect, expect him to behave well, and enforce. Get him into some more manly activities and new big boy responsibilities and don't cut him any slack on the dramatics. Use discipline. It won't take away his sensitive nature, it will just enable him to behave. My cousins raised this way range from quiet, sad, poets to hearty ninja fighters, but none of them milk the self pity. It has to be taught. And if dad is in the picture, he needs to really take charge on this as a manly example and enforcer. The only alternative would be to let him keep acting this way, and I think you're right, it won't play well in Jr High.
