I understand, and that’s why I apologize if I come off as rude. I’m sure you’re not full out encouraging the situation, and as I’ve said – I don’t envy that situation. It’s hard to get over a person you fall for, especially when you get to know them well and when you know it’s not in the best interest of anyone involved to be pining for the person.

Sometimes it’s best to remove yourself from a situation that is causing pain like that though, because simply being involved (even in a passive way) is still encouraging it to an extent. If people are commenting that he’s into you as well, it shows in that alone that there’s something more than a trainer/trainee friendship, and that should be addressed before things happen where he compromises his own relationship.
Have you tried having a conversation with him about it? In being honest with him, you might find more clarity in some aspect of the situation. (Either he may recommend you find a new trainer, or you may find out that he feels the same way and you both need to discuss what happens from there.)
Sitting in a state of “unknown” doesn’t make things any easier, and can make the feelings you’re holding in seem more painful because you’ll always be thinking “what if…”