This will depend on your attachment style, and your partners attachment style. If you're having a lot of difficulty forming relationships, you probably have a maladaptive attachment style.
You want a secure attachment. When you're securely attached to your partner and they're securely attached to you, being in love is kinda just like hanging out with your best friend. There's no nervousness, there's not even anxiety about saying something dumb. You're there for one another, but you don't panic if they don't answer the phone -- there's probably a logical explanation.
From the sounds of things, you're dealing with insecure and possibly avoidant attachment styles. Talk to a therapist, they can help.
Kati Morton is a licensed clinical psychologist and YouTuber. Here's a video of hers on attachment theory
Tons of people are in relationships while having maladaptive attachment styles. By and large, they are less happy by their relationships.