TW: Stalker and obsessive behavior, mentions of possible grooming/predatory behavior.

So, I know this is really far from my usual rants, but I need some help here, here's some context:

I have this one guy friend, we have known each other since the end of middle school and went to high school together, he's a really shy and introverted guy so making friends has always been a really harsh task for him. 

I stared getting concerned about certain friendships he had because of the age gap (around 3 to 5 years, him being the older one) but I let that go since who am I to tell him who he can hang with??

We graduated, he tells me he misses his friends and high school in general, mind you this man was harshly bullied during ALL of HS. We go to different universities and during the middle of the school year he tells me he wants to change unis because his middle school friends (now on high school) are studying there, he sends me a bunch of texts asking how the people on the high school behave, their school hours, their after school hangouts, EVERYTHING, I don't even have friends in high school!!

At this point I get really concerned because in what word is this normal behavior? Anyway, I tell him nothing and leave him on read (very rude of me, but i genuinely didn't knew how to answer) and like two months later he tells me he's changing schools, I get kind of happy to have another friend here just for him to tell me he's not really there for me, not even because he could have better studies, he changed universities because of ONE DUDE, ONE HIGH SCHOOLS DUDE.

And this mf has de audacity to tell me he has been crushing on him for FOUR FUCKING YEARS, FOUR!?!?!?

At this point I'm connecting everything, the weird behaviors, the really odd questions, has this dude been stalking this poor 15-year-old?? And if I do my math here 4 years ago his crush would have been 11, that's a CHILD!! My friend is currently 19, back then he would have been 15!!

I get scared to call him out for this and I stopped talking to him all together, at this point he already made the school change so I would often see him roaming around the halls (specially the halls that belong to the high schoolers), we would have some quick chat here and there but no further contact from there; So imagine my surprise when I wake up to a text of him asking me how he could keep this poor boy by his side for the next year and prevent him from changing schools. I'm sorry, excuse me??

I did tell him that while I enjoy my experience in the uni I can understand why some people may not like it, it's quite a new system and its really group proyect based (so not for everyone), he starts getting really insistent on keeping him on the same masters he is doing, starts telling me about how he is so nice to him and he just can't let go. And I'm like damn can't you just text him every now and then?

I feel like the boy either wants some other place to study or wants to get away from my friend.

Anyway, I think this is (more than) enough context for my recent concern, I want to tell him something useful, make him understand that what he is doing is wrong and maybe ask some help from school authorities for the to intervene in the situation. To be honest I have no idea on what to do with this situation, I could make a report about possible violence but I'm not really sure? Aughhh,  I really do not know what to do, if anyone could help me with some ideas it would be greatly appreciated.

I end of this rant here, won't really decorate because I feel like this is a really heavy topic, sorry for the big rant.

Stay safe buttercup, xoxo.