I’ve been dating Julia (26) for about a year. We’ve been close friends for five years, so she means a great deal to me. We’ve both expressed how this feels like a very serious relationship (talking eventually moving in, marriage, kids etc).

The first few weeks we were dating, Julia introduced me to her “best friend”, a man named Tom (26). Tom was one of five randomly assigned roommates when she moved into the city 3 years during COVID. After she moved out, they remained close friends.

To me, Tom seemed like a nice enough guy. Once I met him, the shallow, kinda lizard part of my male brain that keeps a subconscious lookout for competitors went silent. I saw him as harmless and not a threat at all: he’s a bit of a quiet pothead with a pretty dead end marketing job. He’s not a particularly good looking guy, he’s out of shape, he’s shorter than me, his interests seem pretty limited, and he doesn’t seem to have any ambition other than smoking weed and playing video games.

Julia invited him out with me on multiple occasions the first few months we were dating and I made every effort to be as friendly as possible, trying to take an interest in his job, talking about gaming, his interests in music etc. I even treated his sister to an expensive drink at a food festival (she tagged along) and later covered one of his meals when he realized he didn’t have cash on him(he never got me back). To be honest, he kind of grew on me.

About a month into the relationship, Julia dropped a bit of a bombshell on me: 3 years ago during their time as roommates (during COVID), she and Tom had a month-long romantic fling. They had sex at least twice before she ended things. In her words, the sex was really bad, and they were better as friends.

I’m a pretty reserved/more conservative person when it comes to dating, so this felt like a red flag to me. However, I’m living in a big city now (when in Rome…) and I knew going into this relationship that Julia is more of a free spirit. Plus, it was three years ago, and I’m in love with her now. I therefore have spent months trying to convince myself that it's not a big deal at all.

However, since learning about her past with Tom, Julia and I have been having big arguments as I’ve increasingly struggled to deal with my feelings of jealousy. Basically, situations I previously would have thought were harmless now just drive me up the wall. For example:

• I’ve started noticing that Julia texts Tom pretty much everyday. They talk just as frequently as her female friends. While most of the conversation is shallow, she’s discussed important, more emotional or existential topics with him in the past.
• Julia confides in Tom about significant and private details related to our relationship. In addition to speaking with him about arguments we’ve had, she has also told him about more intimate, private details related to our sex life. For example, one week I thought I was having a serious pain-related sexual problem, which scared me enough to go to the doctor's office. After it turned out that I was fine, Julia laughingly told Tom about the whole mishap.
• When I’m not around to hangout, Julia will go hangout with Tom without me. To me, these hangouts have all the makings of dates: they go thrift store shopping together, they go on long walks, they’ll do silent disco dancing in the park, they get dinner, they might go to a bar afterwards etc. He once hit her up with an extra ticket to a concert (which she accepted) by her favorite singer. She went and told me she had a great time dancing.
• One time when I got out of work early, Julia invited me last minute to a dinner that Tom had previously scheduled with her at a popular restaurant (needs reservations). When I got there, Tom and Julia had started eating already, and the hostess told me there were no more seats, so I left and ate a sandwich at a local deli by myself before meeting up with them afterwards at a nearby bar. Julia apologized, saying she had sent a text (about 5 minutes) before I arrived saying there were no seats left.
• I bought a nice cake pan for my new apartment at Julia’s suggestion because she said she wanted to make me a lemon cake (my favorite). While I was out of town, she sent me a video of her, in my apartment (where I regularly let her stay while I’m out/on a business trip), with Tom and an other female friend with a just-baked lemon cake. When I got home, I found she had left me a box of cut up pieces of leftover lemon cake.
• For Christmas, Tom bought her a purse. It’s not super expensive ($80), and it's definitely a gag gift (on the side it has a meme reference), but it still felt very inappropriate to me. Julia now wears the purse wherever she goes.
• While I was on a camping trip with some friends, Julia was staying at my apartment. On my way back home I asked her what she was up to and she said she had invited Tom over (to my apartment) to watch a movie after they got dinner. By the time I got home, Tom was gone.
• I’ve asked Julia if Tom has dated anyone since they stopped hooking up all those years ago and she says no. He has apparently had a hookup or two with randos from parties, but has not dated at all.

Maybe I’m just totally biased and in my own head here, but to me it feels like Tom is possibly infatuated with Julia, and even if Julia no longer has any feelings (romantic or sexual) for Tom, I can’t help but feel like she’s getting inappropriate emotional validation in some way from their friendship. To me, it literally feels like she has a second boyfriend, and it puts a great deal of pressure on me. As my logic goes, if I’m not taking her out on a date, she’s hanging out with a former lover. If we have an argument, she’s telling a former lover etc etc. I feel incredibly disrespected, and it's making me question everything about the future of the relationship (if we get married, is my wife just going to hang out with this guy she banged and has an emotional connection with? Is she going to introduce him to our kids? etc.)

Julia and I have been fighting constantly for almost a month over Tom and she recently told me that if I gave her an ultimatum to choose between me and him, she would leave me. She insists there is absolutely nothing between the two of them, and that I’m projecting due to my comparative lack of romantic and sexual experience (she insists this is normal for people in the city).

I’m aware that I have many biases and maybe there’s a possibility here where I’m just a sheltered prude who needs to catch up with the modern state of the world, so I would really welcome everyone’s perspective on this situation, particularly folks that are more liberally inclined who may not agree with me. Thank you.