Parenthood Guilt

So my 9 year old son has been in my care since he was 4 months. I tried everything to get his father to bond with him but he just always had an excuse. Anyway he moved on and I moved on. Currently we have lived in Australia for 5 years with my new partner of 8 years, my son and pur daughter. Things have beeb up and down sibce moving but the biggest change is my sons behaviour. We thought at the time he was only 4 that it was just a phase so we didnt think nothing of it. But 3 years later when he was 7 things got worse. He started lying and stealing from us. I am so confused as we have talked to him about right and wrong and he is so well behaved at school. So ok we left it as other parents said its just a phase. But now that he is 9 almost 10. Nothing has changed in fact his behaviour at home has gone worse. I feel for him cause he gets told off everyday about the same things. And my partner is starting to loose his patience because we have tried everything but he just didnt learn his mistake after the first few times and does it all over again the next day. He is also starting to take things out on his sister. We are at our wits end. As a mum I dont want to give up on my son and I want the best for him. But its putting a strain on mine and my partners relationship. The thing is my sons behaviour doesnt only stop with us he is like that with his grandparents, uncles, and my friends too. My partner has now suggested to get my sons father involved and see if there is anything he can do for our son. Because we want him to be happy and not get told off everyday from everybody. As a mum its normal to think from the heart but looking at the facts I dont want to scar my child forever. We are also going to get a psychological test done on him. We love him and feel so quilty but we want the best for him.