Partner of addicted gambler... Don't know what to believe anymore

Hey there, 

I've been looking for answer and scrolling the Internet and it's landed me here. 

Here's the back story... 

I've been with my partner for over a year and a half and we now live together. Prior to moving in together, around 8 months in I found out that he wasnt able to pay his rent (he was renting off a his bf sister and they knew about his addiction) due to being out of work for a bit. It turned out that he had been gambling and wasn't able to keep up with bills whilst being out of work and not having any savings etc 

I didn't know it at the time but I helped him out with some of his bills and he then confesses to me around my birthday that he had been gambling and had got himself into a situation where because he had been out of work wasn't able to pay all the bills (he's self employed bricklayer) so this was the result in it. 

In that moment he pleaded with me that he would stop gambling and do what ever it meant to stop ie I could take over his bank accounts and look at his bank when ever I wanted to and that he would join GameStop. Besides the fact I was devastated at him allowing me to become into debt (on top of me lending him money for rent that time, id also helped him with purchasing stuff for his flat from my Argos card- he didnt even have a bed in his flat when he moved in) I still believed that he was adamant about changing and thought that his addiction was something that wasn't as bad and that he had a handle on it. 

Around December last year and I had moved in with him. I start to find letters from collection agencies to say that he had not paid council tax and various other bills. 

Since then, he started a debt management plan and pays quite a hefty amounts a month. I'm not entirely sure what it's for but I'm assuming it's all of the debts together. 

Fast forward to the other day, Im still quite skeptical as he hides phone screen from me and I walk into the bedroom and I see a roulette wheel glaring on his phone. I know sometimes he plays pool on his phone and has to spin something for this- which is exactly what he told me that was. He obviously jumped out of skin when he realised I was in the room and said that he was just texting a mate first and foremost. 

I told him at that point I don't actually trust him as I feel he's been sketchy with his phone. 

Then again the other day, I had money from my birthday a few months which was stored in a jewellery box. I went in the other week and counted it at 80, then again it went down to 60 and then I looked yesterday and there is 20 in there. 

I'm utterly devastated as I feel like I'm being peddled lies upon lies. I haven't yet confronted him about this situation as Im pretty sure he thinks I've forgotten about this money. 

The one thing I can not wrap my head around is why steal this money from me? Unless he thought Id forgotten about it and he's still gambling? But why take it? 

My mind is in over drive and I just don't know what to believe any more. I feel like I'm just being told so many lies and wonder if he's just gotten better at hiding his addiction. 

I just don't know what to do, as I'm stuck in a lease until July next year. I scared that if I leave I will be chased after and his creditors will come to me if he doesn't pay the bills. 

I appreciate anyone's help or advise in this situation. I love him so much and it's devastating me to have to watch and deal with this. I don't know what to do?