Partner relapse

Im looking for help on how to approach my partner. He had a gambling problem a few years ago which resulted in a prison sentence. We were not together back then but did know each other and I was aware of it happening through mutual friends. We have a nine month old baby daughter and I thought everything was ok until recently something just didn’t seem right with him. My suspicions were right as I checked history on his phone and iPad both had several gambling sites and also PayPal in the history. I did something which I guess isn’t right but I logged I into his PayPal to find several thousand pound’s of transactions of which only half the amount has been paid in by gambling sites. He is obviously loosing more than he is winning unless he has winnings elsewhere. Either way even if I had seem all winnings he still should not be gambling again. I am so worried about him and want to support him but also feel quite cross at the sneakiness and the fact he’s told me several times the last few weeks about a friend who is gambling but that it doesn’t make him miss it or feel like he wants to when all the time he is. I need to bring it up with him before it gets completely out of hand like before. I don’t know whether to speak to his parents who he ended up living with last time after loosing his home through gambling. I don’t want to worry them but also I probably need their support myself. Any advice would be gratefully received.