were jeff and shauna having an affair?

I’m rewatching season 2 rn, and in the episode during Shauna’s labor, we see a pre-crash flashback where Jeff passes a flirty note about a “tutor session” to Shauna (side note: insane to do at the school where your girlfriend and shauna’s best friend attend and was so adored). When I first watched the season, I was half paying attention, so I didn’t really remember it. Anyway, I was under the impression that they hooked up twice, once before the show after the fight that Shauna and ghost Jackie were talking about and then once the night before the crash. But by that note, it makes me think that they were continuously sleeping together and stopped for a little bit, I guess, since Jeff was surprised when Shauna came on to him after the party.