Although there are plenty of external factors that can cause you to feel alone, research has shown that there are certain bad habits that consistently keep people from building strong, lasting relationships.
Pessimism

If you tend to have negative views all the time, you might struggle to keep friends around for long. No one wants to surround themselves with people who are constantly complaining or who always assume the worst will happen.
Negative energy sucks the life out of everyone around you, so they eventually distance themselves to take care of their own sanity.
Guardedness

It’s important to let your guard down in relationships. If you have a tendency to keep things bottled up or refuse to open up to others about how you’re feeling, people will not be able to emotionally connect to you.
In order to have a meaningful relationship with someone, you have to let them in. If you don’t let anyone get close, you’ll always feel alone even when you’re around others.
Self-centeredness

It’s great to love and respect yourself, but if you tend to talk about nothing but yourself all the time or struggle to show interest in others’ lives, you’ll likely find yourself flying solo.
Relationships are about both parties giving and receiving. If you don’t give the other person your undivided attention, show empathy, and validate their emotions, they won’t want to open up to you anymore.
Grudges

Another harmful relationship habit that psychology points to is an inability to forgive. If you’re a scorekeeper or you find yourself unable to forgive others for what they’ve done, you’ll always be perceived as judgmental rather than understanding.
Nobody wants to be around that, which means they’ll avoid you if they don’t feel completely safe and secure opening up to you.
Digital over-reliance

Although social media and text can be good ways to check in with others, you shouldn’t substitute in-person time with your friends and significant other with social media time.
With digital technology, you miss out on reading body language, physical contact, and true eye contact. Deep connection won’t happen if you limit others to screens.
Rigid thinking

Some people have a hard time accepting that others can be both good and bad. If that special someone you’re dating does something that you don’t like, you automatically assume that they’re no longer worthy of your time, even if it was something small.
No one can meet your nonexistent standards 100% of the time, so you’ll end up tossing people out of your life like they’re replaceable.
Passive-aggressiveness

If you feel like you can’t be direct with others about your needs, you may resort to passive-aggressive behaviors: occasional sarcasm, playing the silent treatment, giving backhanded compliments, etc.
Studies show that this type of behavior hurts people more than you’d think. Not only is it unpleasant to be around that type of behavior, but it also destroys any sense of trust between you and others.
Avoidance

Ironically, many people who say they fear being alone are the ones who end up pushing others away first. If you fear getting rejected by someone, you’ll begin to reject others before they can reject you, or you might act cold towards people, so they don’t get too close.
While this prevents you from getting hurt, it also prevents you from getting close to others, something you crave.
Ignoring clues

Some people are just worse at reading social cues than others. Knowing when to talk, when to listen, and when someone needs their space is something you learn over time.
But if you have no social awareness, you’ll talk too much, ignore social boundaries, and not understand why everyone stops wanting to talk to you.
Sources: Please see here for a complete listing of all sources that were consulted in the preparation of this article.