Complex sentence: Mayweather first proposed this when negotiations with Manny Pacquiao first took place in early 2010, which ultimately lead to the fight falling apart due to Pacquiao's unspecific dislike for this type of drug testing.
Split into simpler sentences: Mayweather first proposed this when negotiations with Manny Pacquiao first took place in early 2010. Which ultimately lead to the fight falling apart due to Pacquiao's unspecific dislike for this type of drug testing.