Bolivar felt great pleasure at the liberation of the territory, because it aligned with his diplomatic goals, it represented the culmination of his efforts, and simply because he liked the honors they bestowed upon him, especially the fact that they chose to name the new country after him.

Let's start with the last point. Technically, the one who liberated Upper Peru, as it was known back then, was not Bolivar, but his second in command and protégé, Marshal Sucre. Sucre had won the final victory of the Independence Wars at Ayacucho (and is consequently known nowadays as El Gran Mariscal de Ayacucho) and that sealed the independence of both Peru and Upper Peru. Bolivar, who was trying to create a Peruvian government at Lima, tasked him with liberating the rest of the territory. Afterwards, the delegates that met to form a new Republic decided to name it after Bolívar. By then el Libertador was not simply a military commander, he was a legend, venerated throughout the entire South American continent. That explains why the delegates were willing to adopt his name. In any case, the new country would need a new name - Upper Peru just wouldn't do.

Bolivar was greatly gratified by the decision: "If I receive no other public honours, to give my name to an entire people fills my soul and my heart to overflowing." He also found the scenery of the area beautiful, and, as a man who have always liked adulation and celebrations, he greatly enjoyed the hero's welcome he received when he finally arrived. Perhaps he enjoyed his welcome all the more because the Peruvians were growing tired of Colombian occupation, while back at home civilians were becoming resentful against the "pobres militares", and Bolivar interpreted both situations as an ungrateful people attacking their liberators. In any case, Bolivar also saw the new Republic as conductive to his diplomatic goals and his vision for statemaking: "The Bolivian Republic has a special delight for me. First, there is its name, and then all its advantages, without a single drawback; it appears destined to be fashioned by hand. The more I think of the destiny of this country, the more it seems a small marvel."

Indeed, the Constitutional Assembly had given him Supreme Power and then asked him to draft a constitution for them. He had allowed the Cucuta Congress that created Gran Colombia to draft their own constitution, but he was not satisfied with the result. Gran Colombia was in bad economic and political shape right then, which he thought was a result of a bad and weak constitution. It's important to note that, due to failures early in the Independence Wars, Bolivar felt that federalism and direct democracy were unsuitable for South Americans, and he was firmly convinced that a strong, centralized regime was necessary for the states to remain together and stable. Constitutional resctrictions, popular opposition, and political realities kept him from implementing this vision in Colombia or Peru, but Bolivia offered a golden opportunity to do.

The Bolivian Constitution that the Liberator drafted is kind of an odd creature, incorporating enlightened principles such as the abolition of slavery and separation of powers with the decidedly authoritarian provision that the President would serve for life and be able to appoint his successor. He added a complicated system of checks and balances which, he said, would secure Republican liberty and virtue. But Bolivar himself would not govern under that Constitution. He instead pressured Sucre, a man with little interest in being a statesman, to become President. Sucre accepted out of deference to Bolivar, but made it clear that he would not serve for lie. He found governing under the Bolivian Constitution to be "completely unworkable."

Bolivia also constituted another step in the realization of Bolivar's dream of an Andean Federation that united Gran Colombia, Peru and Bolivia. He forced Peru to accept the Bolivian Constitution, and when he returned to Gran Colombia to deal with a constitutional crisis, he offered that Constitution as a solution to all the ills that were affecting the nation. It's needless to say that the Andean Federation never came to be, but this shows Bolivar's firm conviction that his Constitution was a masterpiece of statemaking.

One of the reasons why Bolivar supported the formation of Bolivia as a separate and independent state was to weaken Peru and prevent its annexation by Argentina. Both laid claims to the land. Upper Peru had been traditionally part of Peru (duh), but in the late colonial regime it had become part of the Viceroyalty of Rio de la Plata (read, Argentina plus Uruguay). The Argentine government had fruitlessly tried to enforce their claim before wars closer to home and civil strife forced them to retreat; consequently, Upper Peru remained under Royalist rule from Lima. The actual power was the Liberator Army, of course, but both Peru and Argentina were anxious to claim the territory for themselves, and with it its rich silver mines.

Bolivar himself recognized that Argentina had the better de jure claim, and he wanted to uphold the uti possidetis principle, which says that the new states were the legal successors of the Spanish Viceroyalties, and thus had claim to all the territories that had been under the control of said Viceroyalties before the Independence Wars. He had used this principle to justify the creation of Gran Colombia as the successor of the Viceroyalty of New Granada. Giving it to Peru would break the principle, but giving it to Argentina "would be to deliver it into anarchy." Sucre understood this, and he called for an Assembly to meet and decide themselves. Bolivar was at first incensed, but he ultimately approved Sucre's course of action because he did not want to allow either Peru or Argentina to take control of the mines, and because the people of Upper Peru wanted to form their own Republic.

Finally, Bolivar also had special affection for Bolivia because it represented the triumphal end of his struggle of 15 years. As he travelled through the mighty Andes to the new Republic, he wistfully remembered all his past glories and defeats, and compared his crossing with that of Napoleon through the Alps. He considered the silver mines of Potosi, long the most productive in the Americans and the main source of the Spanish treasury, to be a great trophy. And though his health had begun to worsen by then, the scenery and the satisfaction of having finally freed the continent seemed to improve his spirit.

In any case, though Bolivar did like Bolivia, he had greater affections for his home state of Gran Colombia. He stayed in Bolivia only briefly before returning to Lima, and when news of political trouble in Gran Colombia came, he did not hesitate to leave and return home. He thought that Gran Colombia was destined for great things and a central place in human history, but he did not have the same expectations for Bolivia. He wanted them to join his Andean Federation, but his greater focus remained the stability of Colombia. Summarizing, Bolivar did like Bolivia, very much in fact, and he felt great satisfaction at the fact that they chose to name the country after him and invited him to write the Constitution. But while he saw Gran Colombia as a special and unique nation, he saw Bolivia as more of a blank slate where he could put his constitutional vision into practice, and he only supported their independence to advance his geopolitical goals.

Sources:

Simon Bolivar: A Life, by John Lynch.

The Santander Regime in Gran Colombia, by David Bushnell.

The Cambridge History of Latin America, vol III, by Leslie Bethell.

Americanos, Latin America's struggle for Independence, by John Chasteen.