As far as I know, Jim said "That's weird" to Spock in the Jellyfish and "That is so weird" to Gaila, and that's all.
I just saw the movie again tonight, and clearly Jim is not referring to Gaila saying she loved him. He starts to explain what he meant; but before he can, Uhura comes in.
I don't think so.
It's the clichee of women overprojecting their feelings for what clearly is only a fling or at best an affair (i can't see young Kirk entering a serious relationship at this phase in his life) so she said the L-word to him and he was clearly taken by suprise.
So his weird line was just the first thing that came to his mind as a way to gain more time to think of something appropriate to say to either claim his "love" without actually saying it or doing the "manly" thing and clarifiying that he just wants an affair with no strings attached (which might get him hit and thrown out of the room in his undies).
Before that came to pass Uhura enters the room and we get on with the movie.