WI am writing this after a long time.

MI made new friends online, and had some good conversations.

Some of them were really good and empathetic guys but some were... Well, you could say, looking only for fun instead of having meaningful discussions.

And tThere were others who taught me valuable lessons in life; by either bytheir good or bad actions or bad.

this is just.a more common sentence contruction.

But oOne thing is clear: human nature is a lotvery complex.

Generally speaking, you don't strat sentences with conjunctions (words like but or and). There are times when it can work, but I wouldn't recommend it here.

I have learned most of thethat most people online were just looking for a backupn emotional support, and when they found one, they used it fully.

I'm not sure what you meant by backup in this sentence, I'd just leave it out. you need a direct object after found - when they found what?

After thatey got the emotional support they needed, they just left because theire purpose had been fulfilled.

"That" is not clear enough here - you need to actualy say what that is or the sentence seems incomplete.

To be honest, I found it amusing, p. People should not be like this.

What I learned was never settle for less in friendships.,

Aand never be dependent on anyone else suchto the extent that your happiness gets attributed tois dependent on that person.

this sentence should be combined with the last one to make it complete. Attributed is not the correct word choice.

If you do depend on someone else for your happiness you will get hurt badly.

If you do what? you need to say.

I found some people online were very reluctant to open up, even after I had great and positive conversations with them.

very reluctant to what? you must say otherwise the sentence doesn't make sense.

It seemed to me that theyse people were not ready to be vulnerable.

Who is they?

When you are growing up and you are young, I suggest you to be vulnerable to be able to grow.

when you are growing up you are young, so saying, "when you are growing up and you are young" is uneccesarily repetitive.

If you think you can avoid pain and suffering by hiding your inner self and not admitting that you trust people easily, then you're most likely to be misunderstood and you'll never have a chance to experience different aspects of human nature.

WI'm writing this after a long time.

The subject "I" is missing, though in very casual situations such as when texting, your original sentence is acceptable.

Made new friends online and had some good conversations.

Alternatively: "Made new friends online, had some good conversations." By the way, in this case, I think the subject "I" can indeed be omitted.

Some of them were really good and empathetic guys but some were... Wwell, you could say looking only for fun instead of having meaningful discussions.

"Well" should not be capitalised because it does not mark the start of a new sentence: "you could say looking only for fun..." is not a complete sentence in itself.

We might capitalise the word after an ellipsis in a phrase like "Some of them were really good and empathetic... Actually, most of them were only looking for fun." Here, both "some of them..." and "actually..." are individual sentences in and of themselves, so "actually" is capitalised.

And there were others who taught me valuable lessons in life eithrough their by good actions, good or bad.

I rewrote the second half of your sentence to make it sound more natural. The unnatural points in your original sentence, in my view, were "by...actions" (as opposed to "through...actions") and the use of "actions" after "good" but not after "bad".

But one thing is clear: human nature is a lotvery complex.

Alternatively: "human nature is a lot more complex than I thought."

I have learned (that) most of the people online were just looking for a backup emotional support and when they found one they used it fully.

"Found" needs an object to attach to.

After that they just left because theire purpose had been fulfilled.

The subject "they" is missing.

What I learned was to never settle for less in friendships.

Alternatively: "What I learned was: never settle for less in friendships."

When you are growing up and you are young I suggest you to be vulnerable to be able to grow.

We don't use "to" like this. I have provided some additional examples below.

"I suggest you eat." ✅
"I suggest you to eat." ❌

"I suggest you run." ✅
"I suggest you to run." ❌

"I suggest you be more mature." ✅
"I suggest you to be more mature." ❌

If you think you can avoid pain and suffering by hiding your inner self and not admitting that you trust people easily, then you're most likely to be misunderstood and you'll never have a chance to experience different aspects of human nature.

A comma would be good to break up this lengthy sentence and make it easier to read.

:) ¶
I'll be sharing what I learned in the coming days.

Some of them were really good and empathetic guys but some were... Wwell, you could say looking only for fun instead of having meaningful discussions.

And there were others who taught me valuable lessons in life either by good or bad actions or bad.

But one thing is clear, human nature is a lotquite complex.

I have learned most of the people online were just looking for a backup emotional support and when they found that, they used it fully.

After that, they just left because theire purpose had been fulfilled.

What I learned was to never settle for less in friendships.

If you dothat, you will get hurt badly.

When you are growing up and you are young, I suggest you to be vulnerable to be able to grow.

If you think you can avoid pain and suffering by hiding your inner self and not admitting that you trust people easily then you're most likely to be misunderstood and you'll never have a chance to experience different aspects of the human nature.

Experienceing and learning is worth the pain and suffering.

:) ¶
I'll be sharing what I learned in the coming days.