I have become way too careful in social situations, and this is extremely frustrating

I am 32 years old, and when I was in junior high school I was the kind of guy who was always very spontaneous and relaxed, and this made it very easy for me to get new friends and to become popular among the girls and things like that.
However, some times in 2002 I gradually started to become more and more "serious" and socially awkward (I think that my parents' divorce that year was one reason, but also the fact that I entered high school and lost lots of my old friends from junior high school) and this caught me in a vicious circle where I started spending more and more time for myself - I did sometimes hang out with old friends and have a lot of fun with them, but this became more and more uncommon until I became depressed for a couple years.
I managed to get rid of that depression some time around 2009 I think, and I started to feel a lot better for a few years and had a relationship with a girl for a while, and for a while I felt genuinely content.
But in 2015 I entered college, and in the beginning I noticed that several of my classmates liked me and tried to talk to me and invite me to parties and things like that, but I was still a bit too careful and always skipped everything, until they stopped trying and seemed to become intimidated by me instead (and I never meet them any more since I took a one-year break, so I am one class behind right now and don't really belong to any particular class, since I have a few important unfinished courses that I am trying to catch up on).
This has made me become a real loner there, and I never spend time with anyone at all at my university (and my university is more than 500 miles away from home).
This is starting to really make me feel extremely frustrated, partly because I feel that I could easily become my "old self" in the right situations (that is, in situations where I have a concrete reason to talk to other people) and also partly because it makes me feel an almost overwhelming longing for the times when I did feel confident and had several friends and was considered an overall cool person.
And I don't know quite how to get out of this either, because the times when I do try to act confident it will always feel fake, and I quickly lose that initial small confidence if they don't play along quickly enough, and then I am back at square one again.

It's much easier for me to be my old confident self when I meet my classmates from junior high school, because they actually expect me to act that way, so I don't feel held back in the same way among them.

Do you know any good way to get rid of my anxious behaviour at my university, so that I can start acting like my old spontaneous self there as well?
I have considered joining some social club, like fencing or something (I know that they have a club like that there, and I have always considered trying out something like that anyway) just so that I can start to meet people there and learn to become confident among them, and in a setting where we actually do something fun and entertaining together instead of just sitting and doing serious school work.

Hi Peter86. I think working on this issue with a therapist and joining a support group may be helpful. Also, I learned that a triple-column journaling is helpful in sorting out your feelings. Please see the following link.

CBT Technique: Using the Triple Column Technique to Change Your Thoughts To Change Your Life! | Psychoeducation in Psychotherapy

And your idea about joining social clubs and activities are also great! Finally, knowing that what you are feeling is a natural reaction to what you have gone through, may help you to feel less stressed about it. I also struggle with trusting people after I trusted them and the outcome was not so good. But we need to take one day at a time, since overcoming these issues cannot happen overnight.

Thanks for posting! I think your experience resonates with some people.

Thank you, that sound interesting.

I think one of my biggest hangups when it comes to "negative thinking" at the moment is that I have become obsessed with making the same kind of positive impression as I did when I was at a camp school in 1999 (junior high school in Sweden starts at age 13);
we were at a ski resort in the summer, and right after I had got off the buss I started flirting with a girl I saw in one of the other buses, and I was later approached by that girl and several of her friends in a minigolf queue and asked to join them in that game, and then I would occasionally hang out with them a will at the arcades there.
Then the second day I was heading for a school party and some strangers asked me if I wanted to join them because they thought I seemed to be by myself, but I was a little too shy for that so I said that I was in a hurry somewhere or something like that.
Then at the school party I started flirting with another girl there, and she also came up to me with several other girls a little while later, and then I got one of their phone numbers but never called for some reason.

I think that those three days at that camp school have made such a huge impact on me because I experienced lots of fun things in a short period of time in a new environment, and also felt a mutual interest in other people, whereas nowadays I feel kind of bored a lot of the time and feel like both I and other people feel uncomfortable during our interactions.
And I feel like if I don't immediately make a consistent positive impression then I would become discouraged and lose confidence in myself, like I have lost some part of my old personality and will never get it back or something.
I even have made positive impressions on several people at my university on different occasions, but for some reason they always feel like "the very last time".
I even got a warm reception from a few invigilators last time I took an exam just about a week ago when they talked to me, with smiles and some physical contact and stuff, and that gave me a confidence boost for maybe one minute.
So there is definitely something weird about my whole mindset.

I can relate to your struggles but at least you recognize the problem now. Social clubs are an excellent idea

Thanks, MickeyCheeky.
I will try my best when I get back to my university some time next week (I travelled home a few days ago to visit my family, since I currently have a short break between study periods).

My current "plan of attack" is to actually show up somewhere where some of my former classmates will be waiting for a lecture to begin (I can find their schedules quite easily on our student page), and start a quick conversation with them there.
I know that some of them liked me in the beginning since they approached me with a smile and started conversations several times before they became insecure around me, and it has always annoyed me a lot that they have got that impression of me.
It would mean a lot to me if I could start conversations with them at some point and show them a bit of my real self.
I feel like this might be a good first step.