Get over a old guy in a new relationship

I talked to this guy for about 10 months. We never officially dated bc he had many problems and so did I. We were broken people but we knew we couldn’t get enough of each other. I can’t say i fell in love w him. But I definitely fell in love w the idea of him and what we could be. I thought he was it. I thought he was my one. But we constantly argued over small things and misunderstandings. So he finally swallowed the hard pill I refused to and stopped talking to me. We blocked each other. I’ve never experienced a heartbreak but that’s what I endured. For months and months I felt empty and incomplete and I missed him every second. I let’s 4 months pass before I could even think of talking to someone else. And i did fairly quickly I found someone he’s amazing the opposite from the first guy. He asked me to be his girlfriend and I said yes. He makes me very very VERY happy. But every so often I think of the first guy. Even in this new relationship I still miss him and every so often cry bc of the amount of longing I have for him. I know, it’s not fair for my boyfriend now. And we have wayyy to much planned for me to break it off w him. Ik it’s fast but we are relying on each other for certain things. And I can’t do that to him. How do I heal from the first guy but still have a relationship? When I’m w my boyfriend I never think of the other guy. It’s when I’m alone and bored he creeps into my mind. Ik I’m horrible but how do I get over this?