yes the scene with tia leads you to think Jamie is bi but it's more like her, the Mc and someone else at that moment, I don't see her as being in a relationship with someone else without the Mc, at least that's my impression, and from what I understand it would be more of a Shauna and Jamie, it's kind of weird how I'm phrasing it but I mean I see Jamie only doing things with someone else only if the Mc is involved.
I don't know if it happens in the 2 versions of Shauna in the cheating path but when Jamie tells the Mc that he can be with Shauna it's like a fresh start and you can see how Shauna is uncomfortable at first and then with Jamie's help she gains more confidence, but after that it's like it's normal to be the 3 of them together in bed so I don't notice too much discomfort with his body from then on, until the scene where Skye touches her waist that reminds you of her body confidence problems because before that everything seemed to have been overcome, going to the point yes Jamie was a big factor in Shauna growing to accept her body (female Shauna that I remember is not emphasized so much in her discomfort, not taking into account its past but its present) but they just seem more like best friends and not with an interest beyond that, the only situations that make you think that it was coming are forced actions (the kiss and the Mc's request) but in my opinion none of their interactions make you think that they could develop a romantic relationship.