I thought just this sentence should be enough. Sorry.
Here is the situation----
Kathy is Chandler's best friend----Joey's girl friend, after Chandler and Kathy kissed, Kethy said, 'I like Joey a lot, but with you...'
Chandler: (Interrupting) Oh, no! don't! See, you're getting me confused, I'm starting to urn.
Kethy: I'm sorry. If you wanna pretend that nothing happened, I can try.
That would mean that he was starting to change his mind about something. Would that fit?
That is the only thing I can think of. Someone else may have a better idea.
Edit: I just did think of another "I'm starting to yearn...."
This would mean that he was beginning to want something, but he stopped before he finished the sentence. It seems possible in context, except that "to yearn [for something]" is slightly old fashioned, and not what we would expect him to say.