I've been in back to back relationships since I was in middle school—sixth grade, to be exact. And before you start thinking that they weren't real because I was so young, remember that those younger than you are people, too.
I wouldn't say I have many regrets in my life, but I do regret throwing myself into the amount of relationships I was in. I don't have enough fingers to count all of them. One could say that it's made me who I am today or that it taught me valuable lesson. Although they're not wrong, I was made to believe I was broken for a long time. I couldn't stay in love with anyone for too long, and the thought of being committed to one relationship terrified the hell out of me.
People tend to dismiss those with commitment issues or try to "fix" them, especially in movies, TV shows, and other forms of media. They're labeled as assholes, players, and everything else under the sun so others' poor opinions of them can be justified. I can guarantee most of those with commitment issues are not trying to hurt anyone and are working through their (very real) mental health problems.
People with commitment issues believe they are not "destined" to find romantic love. They believe they are broken and can often feel isolated. (This does not include people who are aromantic or those who are in polyamorous or open relationships, though these feelings can still apply to them as well.) Society puts so much unnecessary pressure on finding "the one" that it erases the love that's more important: self love.
Self love is an ongoing process, just like happiness. Some days are better than others, and it is definitely not constant. You find the little moments. The moments that last for a second or a minute that make you so glad you didn't kill yourself that one day, that it didn't work, that you're still here, living, breathing, alive. And just like anything else, it is not something that is done without help. Therapy, friends, loved ones, are all important on the journey of continuous self love and happiness.
I had to figure this all out the hard way. I still hurt myself, still have days where I wish I was dead, or dying, and I had to figure this out on the (almost) year off from romantic relationships. While I was believing that I was broken, I was figuring out through giving others relationship advice, to put myself before, or at least equal to, my partners. I realized that no one is worth more than my life, and no one is worth more than anyone else's, either. This is also an ongoing process—you don't just figure these things out and stay fine for the rest of your life. You forget things, re-realize others, and above all else, you keep going. Fight tooth and nail for yourself. You will fail, but you will also get back up and do it again. If you have to lose anyone along the way, remember that it was their loss, not yours.
In some ways, I still believe I am broken. But the difference between then and now is that I believe I can be put back together. I wouldn't necessarily say I believe in myself, though I also wouldn't say I don't. It's not a conscious thing—it almost never is. And, again, belief in oneself is an ongoing process, like self love, happiness, and the little things you figure out about any kind of relationship you find yourself in.