As an 18-year-old woman, I can't shake the feeling that my boyfriend, who's 19, still loves his ex more than me. Am I just overthinking this, or is there something more going on?

We began to get to know each other while he was still in an on-and-off relationship with his ex-girlfriend. At that time, we were just friends with no romantic intentions. After they broke up for a while, we started spending more time together and officially became a couple four months later. Initially, everything felt great, but soon I realized that things weren't quite what I had anticipated. We used to have so much fun together, but once we entered a relationship, we began to notice each other's flaws and became more considerate of one another. One day, while going through his playlists, I stumbled upon a newly created one that included a description expressing his feelings of missing his ex and asking for a second chance. When I brought this up to him, he explained that it was just a moment of stress and admitted it was foolish. I chose to overlook it, and we continued dating. As time passed, I began to notice that his expression of love for me was quite different—not in a positive way—compared to how he treated his ex. In my opinion, the best way to request something is to treat people as you wish to be treated, without appearing needy. I shared my feelings on social media, wrote him heartfelt messages, and even made playlists for him, but he didn’t reciprocate in the same way. He hadn’t even completed the gift for our anniversary or saved the playlist I created. He had done those things for his ex, but not for me, and it's difficult to bring this up with a partner. His ex also mentioned that he wrote her emails during our situationship, but he claimed they were generic messages meant to spare my feelings, and I chose to trust him and continue our relationship. Despite having numerous arguments in just three months, we still managed to work through them. However, I later discovered that he had been texting his ex, saying he wouldn’t leave her alone, but I kept that information to myself. Throughout our relationship, he has sometimes hurt me, but I tend to blame myself for taking his jokes too seriously or for being unaware in certain situations, despite trying my best to make him feel seen and loved. I often find myself thinking about his ex, reflecting on our love, and wondering if I'm somehow at fault for his behavior. We're only a few months into the relationship, and already there are problems, which leads me to worry a lot. I love him and don’t want this to become a long-term issue. Is there anything I can do to improve our situation?