I'm not very interested in Scotty, but he's ALWAYS seemed resentful of the Steph and Jeremy thing.
I think it's a sort of combination thing.
He wanted to be the 'showmance' male. Him and Megan didn't ring true as anymore than friends to me, but that would have done, however, Steph and Jeremy garnered far more attention.
Scotty didn't like Steph's part in the whole thing also because she was emotionally unfaithful. But this may be a red herring.
For all it's possible falseness, I think there actually IS some connection between Steph and Jeremy and Scotty is actually jealous of THIS.
Right at the beginning Scotty actually said that he'd been in a couple of relationships and was badly burned, so he decided not to bother and to just shag around.
He insists he's having a FANTASTIC time doing this, but actually I'm not so sure.
Lastly, the BROMANCE angle, is compromised by Steph, who is not only the 'love' interest, but also occupies a lot of this 'spot'. I think Scotty resents this too.
There is no real overt animosity with Steph, but Steph has supplanted pretty much all his possible 'roles' and he does come across as resentful sometimes.
Everyone seems to like him - we hear about him cooking, we hear about him working out with John, but we rarely see him on the HL except in a supporting role.
Now Tiff is giving him attention he may get over it a bit.