I’ll try not to make this too long.

I’ve worked with someone in my insurance job for around a year.
Let’s call him Dan.

Dan is a drug-dealer, on the side.
He’s not very subtle about it, but is clearly not worried about getting caught.
He has an air of confidence, as if he is untouchable.
He can, also, at times come across as likeable and charming … which makes things more difficult.

There have been a dozen or so occasions where Dan has undermined me and made me feel bullied. I sit next to him (not a choice) and on one occasion, I was getting pretty sick of the subtle abuse and felt like I was allowing Dan to walk over me. (i.e. flicking elastic bands at me, teasing me for being vegetarian, calling me queer/fag – I have a girlfriend, but am a sensitive/ somewhat quiet and introverted guy – and following me to the toilets to turn the lights off, literally every time I go).

He’s several years older than me (I’m 26) and comes across as very immature. He’s also a BIG dude, and doesn’t seem to care about anything, or be afraid of anything. He’s often getting told off for using his phone at his desk and sometimes disappears for 40 minutes, though nobody else seems to notice this and the manager is too much of a pushover to put her foot down.

With his drug money, he goes out and drinks A LOT. He often seems like he is off his face at work and it’s embarrassing that he hasn’t lost his job, while other people are wanting to find work.
I try to be understanding of people – he is obviously the opposite of me, and we come from different backgrounds – but I can’t help but resent someone who picks on me constantly.

It tends to only happen when my manager is away from her desk, or off work.
At times, we have banter and I go along with it.
However, sometimes I feel more reserved (suffering with anxiety) and just want to be left alone.
He’ll come up behind me and make me jump, because he is so unmotivated by regular life (my analysis of the situation) and cannot just do what he paid for. I find it affects my concentration a lot, and on my more anxious days, I feel on edge because I’m waiting for the next thing he will do. I end up getting angry and sometimes go home with a headache and beat the crap out of my pillows. Once or twice, I’ve started ranting to my family that I just don’t give a shit anymore. Fuck life, it’s shit (etc).

I’m starting to feel there is no solution, but what would you advise someone to do in this situation?
Running away (i.e. quitting the job) seems like he is winning and I’m not being a man.
Standing up to him or retaliating only makes things worse.
Trying to have an adult conversation and asking him to stop would be moronic.
Asking to change seats would tip him off to the fact he really fucking grates on me.

Ignoring him doesn’t work either. It’s literally like being in High School.
He only works a regular job so he doesn’t get looked into by the police (as I know he has before, following a near prosecution for being in possession of cocaine. Dan wasn’t the only person involved, though, so they didn’t have enough evidence to convict him of anything… he was just under close observation for months).

When Dan once took some of my personal things and wouldn’t give them back while at work (I know, this sounds like the stupidest shit ever), I got fed up and emailed the department manager asking her to speak to him. He gave my things back, but threatened that if I ever got him in trouble, or made him lose his job, he’d beat the shit out of me. I said if he did that, he would find the police on his door step (given the information he has told me, I would be pretty helpful to the cops). In retaliation to that comment, he said I would end up in a box and he knows my address.

Before I stood up to him in this way, he used to say he could find out people’s address.
I thought he was talking rubbish so challenged him to find mine.
It’s probably not that hard with websites like 192.com, but the fact he knows my address makes me feel threatened.

Honestly, I’d love to tell the police about him being a drug dealer.
But I worry something would happen to my family or me.
I don’t doubt he has dangerous friends (a few of his are in prison).
And he’s not acting… he’s taken cocaine at work a few times (he has shown me the magical white powder that seems to give him so much joy) and he has a second (shitty) phone for his drug dealing. He once came to work with over £600 in his wallet (from one night’s sales).

It makes me so angry that he is getting away with this and I’d love to see some justice.
I feel weak and like a little pussy for letting him walk over me, but what the hell does someone do in this situation?

Fear can be so powerful, and there is really nothing I can do.
I just want to know how to approach situations like this, because it could happen again in the future.

If I didn’t know him better (I see him an uncaring and therefore dangerous), I wouldn’t worry about it.
But I think he still holds the time I ‘dobbed’ on him against me.

A customer once complained about him and I saw him write the guy’s address down.
He obviously doesn’t care much for the law.
I asked him if he would really do something, and he said when the person would never suspect it were him.
It’s like something out of breaking bad.

If I tell the cops, he will likely go to prison (because he’s stupid enough to reveal where he hides his money to me) but I put myself and my family in danger.

If I do nothing, he carries on getting away with it.

I feel so frustrated and would really appreciate some points of view.
HELP!
I hate feeling like a powerless boy.