I [20M] have a recurring pattern of losing interest/becoming "less chatty" after 3-4 months of dating. Why do I do this?

I am currently 20M and I’m looking for some insight into a frustrating pattern in my dating life that has been consistent since I was 14. I keep losing interest exactly when things should be getting stable.

The Origin (Age 14, lasted ~6 months):

My first girlfriend [14F] was perfect like she was smart, cute, and understood me. I [14M] broke up with her because I didn't want to be a distraction during her National Exams. I haven't seen her in 6 years, but I still think about her. Her Instagram is a ghost town.

The "Card Game" Girl (Age 15):

When I was 15, I played a card game with a group. I beat this one girl [15F] 1v1 constantly. She was known for never talking to boys (a "sigma girl"), but the next day she was suddenly "all over me." We were together for a month, but then COVID happened and we lost contact.

The Pattern (Ages 16–17):

Since then, my relationships rarely last more than 3–4 months.

• At 16: I dated two girls [16F and 17F]. With the older girl [17F], we were good for a few months, but then I just started losing interest for no reason.

• At 17: I dated three different girls:

• Girl 1 (17F): She thought I was in love; I didn't know how to reply, so it fizzled out (4 months).

• Girl 2 (17F): She wrote a note in my notebook saying she’d liked me for a while. We had fun, but then I stopped putting in effort (4 months).

• Girl 3 (16F): She reminded me of my first GF; it ended quickly (3 months).

The Problem:

I [20M] always follow the same cycle: I’m cool during the "chase," but once the relationship is stable, I feel something weird—like I'm bored. I don't "ghost" them because we are in the same school; I’ll still say "hi," but I become way less chatty and stop the deep conversations. Eventually, they get the hint and we stop talking.

My Questions:

1. Am I subconsciously comparing everyone to my first girlfriend ("The One That Got Away")?

2. Do I just like the "chase" and the "competition" (like the card game) more than the actual relationship?

3. How do I break this cycle so I can actually have a long-term relationship?

TL;DR: Since 14, I’ve dated girls for 3–4 months, then I feel bored/weird and become "less chatty" until the relationship dies. Looking for advice on how to stop this pattern.