This is the reason for all relationships.
The fear of being alone and everything that comes with that
Nope.
Fear isn't what motivates me to remain friends with people I've known since childhood. It's the fact that we can joke with each other and discuss topics in a way where we both walk away feeling like we've gained something. Its the fact that we can have each other's backs and help each other when we need it. There's a mutual respect for each other's beliefs and how we choose to spend our time even if we have differences.
Not everyone is an extrovert, some people are completely content to not speak with anyone for 6-8 hours a day--some people in fact look
forward to the fact that they can do something that doesn't involve people. The most miserable men in relationships are the men who actually are this kind of person, but have succumbed to social pressure and fear to pretend to be someone they aren't. They've put themselves in a situation where they don't get to have that 6-8 hours to themselves and are struggling to convince themselves that it's good actually and they want that. Go 3 days without talking to your girlfriend and see how she reacts to that.
Meanwhile I have friends that I don't hear from or reach out to for over a week but when I or they send a text we can chop it up for a few hours and then respectfully leave each other alone. Most women can't do that and most women can't be in a relationship with a man in that way. I say most because I've met exceptions to that.