I'm sorry your feeling lonely bro, if you have any interests consider joining a local group to make friends/connections. As for the question... eh there's probably a varietybif reasons.

My wife is absolutely my best friend and everything I do is better if she is there.

I am, however, just starting to come off the effects of the pandemic. I have acute social anxiety and thought I had weathered the lockdown well because not being able to go out and do things is my comfort zone. However, as things became less dangerous and restricted, I found that my social anxiety had way worsened (like two extra medications worsened) and it was difficult for me to even do some of the social things I had been used to pre-pandemic.

I was able to ignore it because of my strong relationship with my wife until my only other nearby friends moved to Illinois. That’s when I realized that I had no friends except for my wife, and I was in danger of using her as a replacement for my own social life. I didn’t want to force that unfair responsibility on her, so I decided to try to get back in touch with a friend that drifted, and started going to a local game store to play MTG.

I’m now far outside of my comfort zone, but having a good time netting new people and playing a game that I kinda missed.

I guess the point I’m making is that, yes, it’s easy to fall into that trap of using a significant other as your social outlet, but it’s unfair to them and you should do everything in your power to avoid it.

My wife and I were best friends before getting married. I'm a social butterfly and pop from place to place and she is a ginormous introvert. Neither of us were lonely but loved the adventures we had together. Ten plus years into our marriage and nearly fourteen into our friendship, we still do most things together. Her friends come and go, and she's the one who understands me deeply and more than anyone else on this planet, and yet we find solace in each other, friendship, and a partnership neither of us expected. Marriage is not for everyone, it's a lot of work, it's a lot of trust, but mostly it's not there to fix a problem. If you go into it broken looking for something else, you may never find it. In the end, it takes two complete people to make it work.

Personally, having a partner is not a replacement for friends. There are emotional needs that my partner fulfills that my friends can't and vice versa.

A partner can definitely become a best friend, but i don't think it's healthy to have every role fulfilled by one person as it makes you very dependent on them.

My partner passed away recently and I found myself suddenly alone in the world. A few friends have their own lifes so I joined a hiking group and it was the best decision of my life. Always looking forward to get back on the trail with like minded people where I made new friends. Lots of single people there so yeah we are human and we need companionship.

It's occurred to me that if my wife ever cheated on me, maybe instead of getting upset I could just make friends with her boyfriend. We'd already have it in common that we like having sex with my wife so maybe we'd have other stuff in common, too.