What I Think about People, investing in relationships with others

I realize that I have been putting very little importance on people, on having relationships with people. I have always thought it is just temporary, so its not worth pursuing, putting in my effort to seek and treasure relationships with people. Why should I, when, after 2,3, or 4 years, it will come to an end and we will go our separate ways? I need people just enough to have fun, to chill, to enjoy life for the moment.

I think subconsciously, when I look at people who try hard and put a lot of effort into fostering friendships, I thought I knew better. These people are wasting time. Relationships are temporary. In the end, you are on your own in life. Because I thought this way, I was impervious to issues that come with valuing relationships/people. Why would I feel lonely, why would I crave people's attention, their company, when in the end, I must face life on my own?

But this hasn't been true. I do want people's attention, I do feel lonely, I do want other people's company. And now I admit, I am most happy when I am with other people. I thought I was too cool for this.......how stuck up I am.

What do I do from this? I am still not fully convinced. I still believe relationships are temporary. But despite this, is it still worth investing in it? Why do I feel sad, feel depressed, when I think relationships are not worth valuing?

I don't know.