To me it definitely happened after the first developments of Gillovny. David got married and right after, Gillian and Rodney started dating. If you read their interviews about each other at the time, and about each other’s partners, you can feel jealousy and frustration on both sides. Gillian never got over not being invited to his wedding and not knowing about he and Téa and David would make fun of any guy dating her anyway. In my mind, Rodney was kind of a rebound. A tall hot cute rebound with an 8-pack.