(Serious) Widow here. How do I help my 8 yr old son become a better man?

I'm a widow with a young son (8yrs old). His dad was sickly all my son's life and suffered oxygen deprivation/brain damage at the end, so my son only saw an adult man that was laying down, having temper tantrums, and didn't help. My husband died when my son was 6.
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I was the strong one, and modeled "roll up my sleeves and get **** done" behavior.
Its been two years since my husband died and i've been noticing that my son is not showing the type of behavior that I really want to see out of him.
- he cries when he's not winning at games. He shoves game pieces roughly and makes snotty pouting noises.
- he whines when he does not get his way.
- he does the bare minimum of any task.
- he complains about things like "having to walk too far" and collapses on the ground, whining
- he gets really upset if anyone calls him out on these issues, unable to accept any valid criticism
- he's starting to comment that he's getting picked on (which does not surprise me)
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I call out these behaviors when they manifest. I calmly explain how these behaviors will make people not want to play games with him, will not respect him. I offer him opportunities to step up and praise him when he does. I model hard core "getting **** done without complaining" behavior myself and I am paying close attention to my own behavior to see if I'm enabling him. I've been the one who fixes things, earns all the money, and solves all the problems for their entire lives. His twin (a girl) exhibits the traits that I want to see in an adult (the same ones I'm asking of my boy).
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Advice please, Men. I don't have man in my life that my son can look up to that can call him out on this bull****. I don't want to raise a whiny, wimpy ******* who expect to get his way and won't step up to do a decent day's work.
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Help?
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Source.