Ways to fix self-doubt

Okay so I just broke up with my boyfriend because of nothing he did, the reason I did was because every time I looked at him I felt like he was way way way out of my league and I feel like he deserves someone better than me. He always sends me kind words of affection and it just makes me feel bad so I was wondering if this is something I should try and fix or just keep living like normal. I also don't like to speak up in public situations because I feel really nervous and I think it has some ties to this.