Partner of someone with a gambling addiction - please help

Hi, 

I have been with my partner on and off for almost 3 years. 12 months ago we broke up because I found out he had been gambling and lying to my face about it, I knew he had gambled a bit in the past but this mixed with taking drugs got too much for me and my mental health and I left him. It hurt because I really loved him but had to put myself first in that situation, he kept saying he would change and try and get me back. 6 months ago he reached out to me and said he really wanted to try again. He told me he had changed and wasn’t doing drugs gambling etc so I forgave him and we tried again. We’re now 6 months in to being back together, and I’ve just found out he’s been lying to me and gambling secretly for around 2 months. I’ve had suspicions for the last few weeks and have asked him a few times and he’s got very defensive and made me think I’m paranoid and how can I think he would do such a thing. The lying and the manipulation hurts! 

I will be honest and say I’m very naive to the world of gambling addiction. Because I don’t understand it myself I don’t understand how he could do this after what happened last time. We both really love eachother and have been looking into buying a house. He has mental health problems and was previously in an abusive relationship, before we met. He hasn’t had counselling or support for this before, just trying not to do it on his own. 

Please can someone help me on where to turn to/who we can speak to try and get through this, as well as give me some advice to understand gambling addictions. He has had gamban on his phone but just has been using a different site. 

Are there any positive stories about people that have got through this? I really don’t want to leave him, but if this happens again I don’t think I can go through this again and the lying.