Fanbelt keeps slipping off?

Hi everyone, this is my first post here. I'm really hoping someone smarter and more experienced would be able to help me out. 

I've got a 2001 suzuki Jimny 1.3 petrol m13a. 

I'll preference this with how I got here in the first place, I took the car off-roading recently at Pickadilly 4x4, went through some deep mud/water, and the fanbelt came off. It proceeded to get stuck behind the crank wheel, and hooked over the alternator/water pump. I had no tools and had to drive home like that, which meant that the car did overhead, but by some miracle I didn't break the engine. 

Back to the Fan Belt: 
I'm doing the usual, belt goes over the crank (rather than behind it), around the Water pump, and tightened using the alternator. However the second I spin up engine, the belt comes flying off. 
Now I've gone so far as to over tighten with the belt just in the hopes that that would stop it from flying off, but alas nothing I do stops it. within half a second it slips off the Crank wheel and goes behind it. It stays over the water pump and alternator, but comes off the Crank each time. Is there something wrong with my setup? When viewing the belt from below, it does seem like it's at an angle...? Right now I'm only worried about the alternator/Fan belt, not too worried about the power steering, I've removed that pully for the time being so I can focus on the alternator. 

Here's a video of it coming off from below:  youtube.com/shorts/zJL0AnURc10?feature=share  
And here's a video of a close up of the Crankwheel with the belt on it:  youtube.com/shorts/U9FmzF_fOg0?feature=share

A view of the Belt from below: 




I'd appreciate it if anyone can give me some guidance as to why this keeps happening. I'm eager to get back on the road (or I suppose off of it) 

Thanks!
 

The picture clearly shows the belt running at an angle which suggests the pulleys are out of line, you need to determine why and fix that.

Given the age of the car I'd be surprised if the rubber laminate in the crank pulley was intact. It might feel OK with the tension from the other belt but if you take them both off you shouldn't be able to feel any movement. Another test is with the belts off have an assistant start the car while you observe the pulley for wobble. It's also possible that something is bent like the alternator bracket. And finally and I hate to be the bearer of bad news but once an m13 engine has been allowed to over heat it's highly likely that the head gasket will have failed, they are very susceptible to damage when they get hot but they are usually good at keeping cool if everything is working properly.

First video: the pulley wobbles- start with a new crank pulley, on the M13 there is a major design flaw with the pulley and the belt tension rips it apart. They are either about to come apart or they have just been changed....

Second video and photo: the belt isn't straight.  It won't be if the crank pulley is failing, the belt tension flips the pulley rim sideways, but you could also have a problem with the alternator alignment.


Fit a new crank pulley first, and then worry about checking the alignment. 

Martin sells the pulley in the shop, they are such a common failure that pretty much every online retailer keeps stock as well.

Mine did the exact same a few years ago, put the belts back on and they came straight off. Once I took the crank pulley off it was completely gone, so fitted a new one and all was good.

Thank you for the feedback everyone! 

So it seems my next course of action is to pull the crank wheel off, and see if it's warped/broken and in need of being replaced. 

I'll report back once I've managed to do so... 

Thanks again for all the advice!