need advice

Okay so a few weeks ago, my ex got in a bad car accident and texted my mom after telling her how sorry he is for everything and that he wanted to talk to me. I knew he'd never try to ask for me back since he's head over heels for his girlfriend and I have a boyfriend I love and he knows that so I unblocked his number and we talked it out and I forgave him. So the last couple weeks, we've been becoming better friends and he's agreed to help me get a deal with some work on my car at the dealership he works at. But I didn't tell my boyfriend, he hates my ex even though they've never met and he'd be sooo mad if he knew. I don't want him to feel like there's anything more going on but I'm afraid to tell him and end up fighting over it. I know I need to tell him because it'll be worse if he finds out on his own but how do I tell him without making him super mad?