Please remind me who once tried to build socialism in Angola and Afghanistan respectfully?
Do you really think USSR cared about socialism in Angola? It was a question of supporting one superpower or another. BTW "buliding socialism" in Angola was performed mostly by Cubans.
Where did China get its nuclear technology? India? Iran? Iraq? North Korea? Why wouldn't Castro want a few? Is he worse than other one time soviet clients?
China is a difficult question for me. I need to look for some sources. IMO breaking the alliance with China was the worst Mikita's mistake. BTW, when did China make a first test explosion? IIRC in early 80s they already had thermonuclear weapons.
India and Iran? They do have Soviet and Russian reactors. I doubt that USSR supplied them with breeders. BTW, the dirty American blackmail worked and forced Russia from signing contracts with Iran about new reactors...
Iraq?! They have nuclear technology?! Oh, sorry, your whitehouse looney is going to bomb them anyway... CV groups heading towards Persian Gulf eat too much money to simply turn them away.
North Korea? For them it's a question of national survival. But again I doubt they have breeding reactors bought from USSR.
Please remember that USSR signed a treaty for not spreading nuclear weapons, and, unlike the "land of free", we don't have a nice habbit of spitting on any agreement when it stops to satisfy us. If USSR/Russia helped someone to build a Bomb - then please show us your information and start bombing us like you did with poor Serbs. If you have guts.
So that when Soviet Union turned traitor to the holy work of liberation of international propletariat, joined the enemy's camp and left Cuba all alone (not counting those wacky North Koreans) against the world capitalism, they would have some weapons to bargain with.
Castro should have done anything to please his ally, having such an enemy so close could leave him helpless without Soviet support. And if both USSR and US considered his regime dangerous - nothing could save him.