Isn't Edgar paired with pretty much every male in bad FFVI yaoi, anyway?

I personally believe that there may be enough between Locke and Celes for a relationship (as Locke clearly demonstrates by the end of the game that he's finally ready to leave his past behind and move on). I couldn't say if it'd be a successful relationship or not, but since Celes obviously shows that she has feelings for him, and since Locke opens up to her more after the Phoenix Cave/Kohlingen event, it's quite possible they'd end up together some time after defeating Kefka.

Now as for Terra and Leo, I never really interpreted their relationship as something romantic. Maybe it's just me, but I think Leo being Leo, he felt guilt for what Kefka and the Empire did to Terra, and by helping her, he probably thought he could redeem himself. I think his concerns for her were more akin to that of a big brother figure, or at least that of a good friend. You'll notice that most of the Returners show the same type of concern toward Terra; they know how much she suffered and that she's pretty strong despite her appearance, but they don't want her to get hurt again or feel sad and lonely.

And well, just because the conversation Terra and Leo had on the ship was about love, I don't think it automatically means they had romantic feelings for each other. In a sense, I feel that Leo related to her in that scene. Being a general, he probably never really got into a serious relationship in his youth (if he even got into a romantic relationship at all), so he might have known what she was going through. He wanted to reassure her; Terra's young, and she was under the control of the Empire for so long, it's no surprise she never learned what love is, but she would in time.

Besides, it wasn't really romantic love they were talking about, but what love is in general. >_> Leo had probably planned to talk to her more in dept about how friends and family can show her what love is, but then, we all know what happened to Leo, so that talk never took place.