He was very touchy and very fragile. He ended his life in Rome on August 2, 1667, by his own hand.
(1599-1667) Italian architect. He is one of the most important artists of the Baroque architectural style. He was born on September 24, 1599, in Bissone, on the shores of Lake Lugano, in Northern Italy. His father was a builder. Borromini started his career as a stonemason. At the age of twenty, he went to Rome, where he would later create his most important works and stay for the rest of his life.
Francesco Borromini (25 September 1599 – 2 August 1667), was an Italian architect born in the modern Swiss canton of Ticino who, with his contemporaries Gian Lorenzo Bernini and Pietro da Cortona, was a leading figure in the emergence of Roman Baroque architecture.
In those days, Maderno, one of the important architects of the period, was continuing the construction of the Church of San Pietro. He took his distant relative, Borromini, with him as a stonemason. Borromini was engaged in the making of stone-carved decorations and statues of angels here. But since Maderno saw the talent of the young master, he also employed him in the design of the Barberini Palace, which he had undertaken just before his death. Borromini always had great love and respect for his master, and even stated in his will that he wanted to be buried in his grave.
Upon Maderno's death in 1629, Bernini was appointed as the architect of San Pietro. Borromini first became his closest collaborator, he was involved in the design and construction of the Barberini Palace, which was left unfinished with the death of both San Pietro and Maderno. However, their relationship was not friendly at all. Borromini, an introverted, suspicious, grumpy, and easily offended person, could not bear the successes of Bernini, he saw himself as crushed and pushed aside by him and defeated by the right. Their views on architecture were also different. Bernini was trained as a painter and sculptor, and became the foremost artist of those days, especially in the field of sculpture. He considered this accumulation sufficient to be successful in architecture as well. Borromini, who came from one of the most important steps of the art of building like stonemasonry and was above all a competent builder, found him inadequate in the technical field. In 1633, when the San Carlo family was suggested to build the Quattro Fontane Church, he left Bernini without hesitation. But throughout his life he saw his as his biggest rival, ruthlessly criticizing him at every opportunity. As his mental health gradually deteriorated, he ended his life in Rome on August 2, 1667, by his own hand. He was buried in the Church of San Giovanni dei Fiorentini.
The first building Borromini made as an architect was the San Carlo family Quattro Fontane. The complex, consisting of a church and a monastery with a courtyard, is very skillfully placed on a small and unsuitable plot. Although small enough to fit inside one of the pillars supporting the dome of San Pietro, the Church of San Carlo is one of the most magnificent structures of the High Italian Baroque. The plan of the church consists of a parallelogram with sides of equal length. The corners of the parallelogram are rounded, and the edges are inflated inward so that the interior becomes an ellipse surrounded by an undulating wall perpendicular to the entrance. This solution combines the longitudinal axis scheme, which was widely used in Antiquity, the Middle Ages, and even the Baroque period, and the central plan scheme of the Renaissance in the same structure.
-----------------------------------------
https://www.newworldencyclopedia.org/entry/Francesco_Borromini