Feeling distant from 5 year old son

I’m bawling as I type this.

I have a son with my ex who treated me terribly. We broke up three years ago and now my son rarely sees his father. Fast forward, I met a great guy and we ended up having a baby very early in our relationship. My oldest son was and is still jealous. My oldest son spends a lot of time with his grandma (my ex’s mom) while I’m working. She spoils him to death.

The past few months my sons behavior has been terrible. Talking back, hitting, not listening, all things you can think of. I’ve tried to do time outs and other things but haven’t been working. My bf is getting upset about it all. I’m feeling like I’m becoming very distant toward my oldest son and I hate it. He’s my boy and I love him but the attitude has got to go. It’s my fault for letting it get this way. Any advice? I feel like we don’t bond anymore. :( Any chance we get, he seems to throw a fit or misbehave. I know he’s probably jealous of a new baby and my bf coming into our lives so quick but I don’t know what to do. I try not to “yell” at him but I just need new ways to get him to behave. I feel like I’m ruining things between us. I’m failing as a mother.