Complex sentence: Tripp maintained that most people are heterosexual because their upbringing has made them expect and want to be heterosexual, and that while early favorable heterosexual experiences to help reinforce heterosexuality, there is an uneven correlation between early sexual experience and adult sexual orientation.
Split into simpler sentences: Tripp maintained that most people are heterosexual because their upbringing has made them expect and want to be heterosexual. Tripp considered early favorable heterosexual experiences to help reinforce heterosexuality, but nevertheless observed that there is an uneven correlation between early sexual experience and adult sexual orientation.