(Name change because I'm a coward
.)
I work for a very large organisation but in the certain branch I work in, my team is very small. (The team itself if split into 3 areas, with four people working in each level). We recently (last three months approaching four) hired an apprentice to do secretarial work such as filing, answering phones and dealing with the customers face to face.
He's a young man straight out of University who during the interview was extremely enthusiastic and stated he was looking for an 'in' to begin his career. He had fantastic qualifications (and great character references from his tutors etc).
The first two months we got along fine (not close but he was friendly, eager to learn and would always be quick to offer his help to me and others where he could). But this last month it's like he's a completely different person to me... And only me. When I ask him to do something (I'm his senior) he huffs and rolls his eyes or makes a face.
He also constantly has something / someone else (usually me) to blame when he makes little mistakes in his work, which is never a big deal because he's an apprentice and we expect a few mistakes - what I don't expect is to be blamed for them in some round about way!
I've voiced my concerns to my Manager who has said he will keep an eye on the situation (and he has said he doesn't believe him when he uses me for his excuses so for me not to worry) but despite that it's really beginning to grate on me to the point where I dread coming into work. My Manager is lovely and really was understanding, but was as baffled as me as to why this was happening and suggested that maybe I sit down (with my Manager and this colleague) for a chat, but I don't want to because I know how it will go down (i.e. He will make excuses and make me feel like I'm paranoid about it all!)
To the other members of the team he's helpful, he's nice and eager to assist but now to me he's none of that. He's sarcastic and passive aggressive - but only when it's just him and me. Around others he's fine with me. The rest of the team adore him and although they believe me when I tell them his attitude towards me and things he's said (and they have themselves noticed he likes to judge my work over everyone's very openly) they are only hearing it from me when he's presenting them with a very different image, so I can understand why they can't fully understand.
A friend hinted that I record how he is with me, but I'm pretty sure that will somehow land me in trouble and I'm not sure if it's even legal to secretly record people?? 
The only thing I can think has brought this personality shift is that he mentioned in passing during his interview he has an interest in X career path, one on which I'm in. The thinking of my Manager when we hired him was to also train him to be in my career path like this guy wanted (hence why I'm asked to give him training occasionally on how to do things I do on top of his current job role) to prepare him for this and in the beginning he was very excited and eager for this to happen because it's his dream job.
But during our training he belittles my knowledge of the field of work, enjoys bragging to me he could do work faster than me if he had that project and how if he had my job he'd have done everything he could to be the best and really shine (which he makes clear I don't) He studied my job area at Uni as part of his course and he is learning now about it further at home in his free time so he really considers himself quite the expert, but with no prior experience under his belt actively doing the job he struggled to find a job in it. The apprentice role was the closest he could get.
I feel like he's trying to put me down so much subtly infront of my team (and not so subtly in front of me) so he can somehow steal my position, since he has technically not got a guaranteed job at the end of his apprenticeship. I know my Manager is highly considering him for a full time position afterwards because of how hard he works (and transgressions with me aside he does work very hard within his role and has made excellent relationships with other departments).
I began to dread the occasions my Manager asks me to deliver training because of his attitude and my other colleagues couldn't do it because of their own circumstances. So I've openly stated to my Manager I don't feel comfortable doing it because of the attitude and he agreesd, so said extra training stopped (it wasn't a requirement for his current job role, just an extra) and this seems to have made this co-worker even more bitter towards me, like it's al my fault! I get a few filthy looks now when anyone casually asks why it's stopped.
But I won't feel guilty for that. I won't pretend I wasn't being a little spiteful doing it but I was offering time out of my own day to offer training I didn't need to and he doesn't deserve my favours anymore 
or at least, that's how I see it. Maybe I'm just being petty...
Someone has suggested he may have an issue with me? I understand sometimes people just don't click, but why so suddenly has the attitude changed? I'm really confused. I'm beginning to suspect he doesn't want to wait for the year to be up and is after my job now? I've asked him about his attitude with me a few times and he basically denied it and tried to brush me off and make me feel like I'm imagining things or being paranoid, claiming he 'forgot' if I ever taught him something or have some equally frustrating response and excuse to give me.
I hate being told I'm imagining things, especially when he delivers the speech with a knowing little smirk like he finds it hilarious.
I've spoken to HR, and though they have said they can bring him in to speak to him I don't feel like that will achieve much. He's young and this is his first ever job (other than part time bar work through Uni) but I can't accept how he's behaving anymore and I'm honesty considering asking for a transfer to a different branch to avoid him, but that of course means more travel time for me and I like my team - minus him. The closest branch is an hour shift travel away I don't feel like I should be the one to leave in this situation and yet I can't see how this can be resolved beause I'm the only one really seeing it in its full extent.
What I'm trying to ask is... AIBU assuming he's trying to steal my job?? I just want some reassurance really that his motives aren't just pure shittiness to me because of some kind of character flaw I have, since everyone loves this guy because shittiness with me aside - he really is charming and nice!
(You must know the type - the office smooth talker who could talk his way out of anything! He's not 'good looking' but he's very good with words and talking to people he just meets like they've known one another for years.)