Lose interest when I can have her?

I am 21 male, i never had a serious relationship but i would love to have one.

But everytime i am 100% certain i can have it with a girl my interest just dissapears, i don’t know if i have a subconcious problem or whatever. But it just keeps happening.

Also I can’t get interested in a girl if I didn’t like her first, in my mid teens i wasn’t super pretty but i got a good glow up towards the end of my teenage years and now girls add me, text me or whatever from time to time but i just can’t, they are often great girls but i can’t help it.

Only once i didn’t lose interest, back in highschool and i still know her, have been spending time with her recently and i think i am still into her. She is the first girl i ever liked like that

Lose interest when I can have her?
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