First of all well done in keeping well. I trust your leukemia treatment has been successful and you are keeping well.
Secondly – it seems that you managed to stop gambling for several years – so that is encouraging. If you can do that once you can do that again.
Thirdly – you recognise that you have a gambling problem and the solution is not to gamble – ever! Not so hard to do. Life doesn’t stop because you are not gambling, just like you looked after yourself with you illness and didn’t do some things – so not gambling will keep you well, mentally as well as financially.
As your girlfriend has “found out” about your gambling, I wonder if you can get her involved in your recovery. One of the things you need to do is lose access to finance. If your girlfriend can take over your finances for a while until you feel stronger – this will make things easier for you. You also need to lose access to the places where you gambler (info on internet site blockers etc are elsewhere on this site) and you can ask to be barred from physical gambling locations.
If you can attend one of the facilitated groups on Mondays and Thursdays here, you will get more information and support … I wish you well.