Does Minerva McGonagall love Albus Dumbledore?

Minerva McGonagall does not love Albus Dumbledore romantically.

She loves him only as anyone would love a very dear friend.

Details on her relationship with him:

Minerva knew Dumbledore for the majority of her life. She attended Hogwarts as a student during Dumbledore's time as Transfiguration Professor and even replaced him when he took the position of Headmaster of the school. She served for many years as his Deputy Headmistress, standing in for him and even replacing him as Headmistress on several occasions.

Minerva had great faith in Dumbledore, placing great stock in the differences between him and Voldemort. However, she did not hesitate to disagree with him when she felt the need to do so. She greatly opposed his decision to place Harry Potter with Petunia Dursley and her family, calling them the "worst sort of Muggles imaginable." She also served more than once to bring Dumbledore back on track when he became distracted from the matter currently at hand.

Minerva had no qualms displaying her loyalty to Dumbledore. When Cornelius Fudge brought Aurors to arrest Dumbledore in 1996, she boldly stepped forward and announced her intention to fight the Aurors on his behalf. She only stepped back at Dumbledore's insistence when he reminded her that Hogwarts and her students would need her in his absence.

Minerva was devastated when Dumbledore was killed in 1997 during the Battle of the Astronomy Tower, and attended his funeral. A year later, when Harry Potter returned to Hogwarts on a mission given to him by Dumbledore, she did not question the decision of her dead friend, but immediately sought to provide whatever assistance she could.