Ideally, the Guru should not be aware of mundane distinctions. They can then best focus on the truth. If a beautiful young female disciple is more interesting to them than an old worn out man about to die from disease, then they are not seeing the equal spirit, but the unequal external body. This leads to serious problems in spiritual movements. The woman is the power of Maya over man.
Man becomes bewildered just by thinking about the form of woman if lust remains in the heart.
Therefore, the Guru, the real one, is very rare. You have not said that the Guru has broken serious Vedic principles. You ahve only said that he got heavily involved in someones life, then ducked out of the relationship when the going got tough, and failed to follow through on promises made. No, this is not breaking some hard and fast Vedic principal that we can point to, but in my opinion it comes from breaking a whole bunch of little ones. For example, in the example, a woman is involved.