Hi Lolly
I don’t think many (if any) of us didn’t feel the necessity to resort to checking up on things that worried us and made no sense.   I cannot tell you what to do but in my opinion, I think it is best you keep the fact you are checking to yourself or you risk sending him further underground with his activities – definitely don’t feel guilty.   Don’t worry – when the shadow of the addiction to gamble passes the investigative person you feel you have become disappears.  
There is no loss that is too small with the addiction to gamble.   Any gamble keeps the addiction alive because the addiction has nothing to do with money – it is what it does to the mind of the CG that causes the damage to the CG and those around them.
Sadly his gambling will get worse without the right treatment.
At the top of this page click on to ‘Resources’ and in ‘Location’ scroll down to ‘world’.  Click ‘Gambling help’ and then ‘Search’.   Scroll down to ‘Gamblers anonymous – Twenty Questions’.  Most compulsive gamblers will answer yes to at least seven of these questions.   In my opinion most members who have lived with the compulsion to gamble will also be able to answer yes to at leave seven of those questions which hopefully will help you ‘know’ what you are of are not dealing with.  Perhaps you could print them off and tick the ones ‘you’ know deserve a yes and maybe he will realise that you are aware he has a problem and you are taking it seriously even if he isn’t.  
CGs can believe they can stop to suit themselves but I’m afraid that no matter how many ***** your partner swears he can do so, until he really wants to commit his life to being gamble-free – he won’t.
You cannot save him Lolly but as Monique has said, you have made a giant step towards your recovery by writing on this site.  The more knowledge you gain the more you will be able to cope.  The only person you can save is ‘you’ and in doing so you will be doing the best thing for your partner.   I wouldn’t be writing on here if I didn’t know that the addiction to gamble can be controlled.