My irrational jealousy over my girlfriend's friendship with a guy is affecting me and our relationship.

So my (m21) girlfriend is amazing, she's kind, loyal, cool, pretty, smart and all kinds of amazing. I met her in college, where we are part of the same program. We became friends first, remained friends for like a year before getting into a relationship.

So she's friends with this guy who is also part of our program too. They also work together so they spend a lot of time with each other, they kinda have to. They are also very good friends, they have their own funny nicknames, jokes n stuff, kinda like we used to have before our relationship. Their homes are also nearby so they'll sometimes go home together sharing the train or the bus, which I can't because my home is further away.

She has never given him time or attention at the expense of me, she has never made me feel unloved or ignored, she has gone above and beyond to show her love to me, she has constantly made me feel loved, seen, heard, appreciated etc. I have no doubts about her and this guy, she's a really good person, too good for this world.

But when I see her spending time with him, laughing with him or smiling with him, asking him to help her in academics instead of asking me, seeing her insta stories with him and all this, makes me feel incredibly jealous. I know this is extremely irrational, she's friends with him and she's a very friendly person, but it still makes me feel really sad, paranoid, angry seeing them together. I have never brought this up to her, if I ever do, she'll either become enraged at me for doubting her (which will be justified) or she will become really sad and apologetic and reduce her communication with this guy, no matter what happens, I end up the bad guy. I have tried so hard to ignore it, to forget about it, to try to rationally think it through, but no matter what I still feel like this, then end up feeling extremely guilty.

What is it that I should do? I don't want to lose her, and I certainly don't want her to think of me as some paranoid insecure narcissist freak. Thank you for the help.