Do I need to break up with him?

Sooo long story short my mom set me up with this guy (her best friends son, we are friends with their family pretty much). We have been dating a month and are already super serious which makes me nervous. Probably about a year before I started dating this guy, I got out of a breakup that was really sad for me. I was in love with my ex and he left because he said he needed to get over some personal issues with his family.

Recently my ex reached out to me. I didn’t entertain the conversation, I left him on read. I have a boyfriend. But him reaching out to me made me realize how DIFFICULT it was to not talk to him. I didn’t realize I still had those feelings for him, I didn’t realize I still loved him. If I knew that, I would not have gotten into a new relationship.

Now don’t get me wrong I know my ex probably just being stingy and he’s probably talking to 3 other girls and I know we broke up for a reason and I don’t want to get back together. But now I literally feel sick to my stomach because I just realize I love some guy who I’m probably never gonna be with and I’m dating this new guy. I’m not sure what to do. This new guy I’m dating is sweet as can possibly be, but if I’m still thinking about my ex, does that mean he’s not the one? How do I know if someone is right for me?