I want to talk about this topic because many of these thoughts have been ruminating inside my head during the wholeall day.

technically correct, but "all day" sounds a little more natural!

Although I just graduated, I never felt I fit in that placere.

That was a public university, and it was difficult to pass the exam to get intontrance exam.

My family also advised me to choose the easiest path, and they did not support thate risky choice.

Some years later I met the person who would become my boyfriend, and guess what?

He is studying at thate university I wanted to go to.

"that" is used more for comparisons - "the" is simpler and sounds a little more natural!

Sometimes he shares with me all the wonderful people he's met and experiences he'd hasd there, and I feel sad.

I would like to reverse the time and tmake another decision, but simultaneously I think about all the things I have experienced (not at my university but outside) and I want those memories as well.

I want to talk about this topic because many of these thoughts have been ruminating inside my head during the whole day.

To make it sound more natural, I’d suggest the above. You could also replace “the whole day” with “all day”.

Although I just graduated, I never felt I fit in that placere.

You could also say “fit in in that place”, but that doesn’t really flow particularly well, so it would sound better to replace “in that place” with “there”.

I knew that I did not want to be there, but I also I didn't have the courage to apply to the university I wanted to go to.

“Also” often sounds better between the subject and verb.
“to go” refers more so to leaving a place, but “to go to” refers to going to a different place, which is what would apply to this situation.

That was a public university, and it was difficult to pass the exam to get into it.

Although that starts sounding a bit wordy at that point, so I would suggest “it was difficult to pass the entrance exam” or “it was difficult to get in”.

My family also advised me to choose the easiest path, and they did not support that risky choice.

“That risky choice” sounds a little weird here, but I’m not sure how to reword it.
What I might suggest is to elaborate on what “that risky choice” is referring to.

SomeA few years later I met who would become my boyfriend, and guess what?

“Some years” sounds better by itself, when you’re talking about a particular (usually small) selection of years (for example “Some years are good”). “A few years…” would be better when talking about a certain time in relation to another point in time, such as in “a few years later” or “a few years ago”.

He is studying at thate university I wanted to go to.

“The” sounds more natural here.

Sometimes he shares with me all the wonderful people and experiences he has there, and I feel sad.

Another possible way to word this that might sound a little more natural is “Sometimes he tells me of all the wonderful people and experiences he has there, and I feel sad.”

Thatis is because I get overwhelmed by the thought of all the things I miss simplyed out on because I did not take the chance to try.

“This” is optional, but I personally prefer using “this” here.
“I missed out on…” sounds a bit more natural too.

I would like toish I could reverse the time and tmake another different decision, but simultaneously I think about all the things I experienced (not at my university but outside) and I want (to keep) those memories as well.

Optional - “I would like to” could be replaced with “I wish I could”, which is more natural.
“The” is not used when talking about reversing time.
You would “make a decision”, not “take a decision”.
“Another” can imply that you wish you could make a new decision in addition to the old decision, but “a different” always means that you wish you could replace your old decision with a new one.
Optional - adding in “to keep” would clarify what you mean.

I want to marry my boyfriend soon, and perhaps I wouldn't have met him if I had made another different decision.

Both make sense

I want to talk about this topic because many of these thoughts have been ruminating inside my head during the whole day.

I want to talk about this because it has been running inside my head the whole day

Although I just graduated, I never felt like I fit in that place.

I have always felt that it was not for me, ands it did not inspirleave me with anything more than repression and gray blocks.

I knew that I did not want to be there, but also I didn't have the courage to apply to the university I wanted to go to.

That was a public university, and it wais difficult to pass the examntrance exam (OR it is difficult to get into.)

My family also advised me to choose the easiest path, and they did not support that risky choice.

My parents did not support that risky choice, and advised me to choose the easiest (OR safest) path.

That is because I get overwhelmed by the thought of all the things I missed simply because I did not take the chance to try.

I would like to reverse the time and take anotherchange my decision, but simultaneouslyat the same time I think about all the things Imy experienceds (not at my university but outside) and I want to keep those memories as well.

That is because I get overwhelmed by the thought of all the things I missed (out on) simply because I did not take the chance to tropportunity.

I would like to reverse the time and tmake another decision, but simultaneously I think about all the things I experienced (not at my university but outside) and I want those memories as well.