How can I overcome my relationship anxiety

Ok this is going to be a bit of a long winded message so please bare with me and as always your help is greatly appreciated. I am extremely anxious when it. Comes to relationships and my anxiety was one of the reasons that my ex boyfriend and I decided to call it a day. We were together for 4 years and I thought that he was the one. After breaking up I didn't want a relationship as I was upset and also because I knew that they make me feel anxious and I just wanted to concentrate on overcoming my anxiety and having fun as a 23 year old. I quickly found myself having a rebound but at the same time I was getting very close to another man. He is an incredible man but I wasn't exactly sure what was going on between us as he was having some health issues and said he didn't want a relationship j til he knew what was happening. I then found myself having another one night stand after all of this. I felt terrible about it and I was very drunk and very confused. We have now found ourselves spending a lot more time together and have given a relationship a go. Now he has stated that he believes we have been in a relationship since I first went to visit him. I have written a previous post about this as I don't believe you can be in a relationship with someone unless you have spoken to each other about this. Now I feel like I have cheated on him (this is one of the very bad intrusive thoughts I get when I am in a relationship as I could NEVER do that). I don't k ow whether I should talk to him about it all incase he says I have cheated on him it whether to just keep it to myself as a friend suggested. Have I cheated? Am I a terrible person?