Hi D,
Well done on looking for help.
First the bad news – it is a GAMBLING addiction. Whilst it is the online sports betting that has brought you here you will find it very difficult to stop doing this while still visiting the casinos with your uncle. If you continue gambling with your uncle then even if you manage to stop the online betting the addiction is more than likely to just switch to another form of gambling.
Now the good news, you can stop gambling. Read the other stories here – you will see the sort of things that have helped others, you can apply them to your own situation.
How else can you fill your time?
It will help if you are honest with those around you – your uncle needs to know you have decided to stop. Your mum or girlfriend could help with accountability. You already say that your mood swings effect those around you – if they don’t know about your gambling then they probably know there is something wrong anyway.
Keep posting.