The way the dark haired Slayer reacted in regards to having to cast aside a comrade immediately struck me as the kind of person who would be happier in FT than in ST. Especially after what his Exceed said.
This. If you're a Dragon Slayer with an Exceed, you end up in FT. If your a Dragon Slayer without an Exceed, you end up in FT and then you get an Exceed.
In fact, so far the poison guy is the only Dragon Slayer we've had that's not in FT, and he wasn't an artificial Dragon Slayer.
I feel like the series is set up to be this obnoxious chain of unrequited affection.
Juvia like Gray who likes Erza who likes Jellal. Lucy likes Natsu who likes Lisanna etc.