<human>: my girlfriend and i met over a dating app. we were both 'in love' slightly over the app, that's why we decided to meet. so, we met and ended up in a relationship.

she said she didn't like me as much as she'd thought the first time we met, but after a while she warmed up for me and we're very close now, and she says i'm the person she's liked the best out of anyone she's dated.

now, my problem is that she lied about meeting a guy. i tricked her into telling the truth, which made her very angry and desperate where she tried to say she 'didn't remember'; which is find so unlikely it's not really possible.

so, basically she met and fucked a guy after we met for the first time. if she met and fucked someone before i met her physically, it'd be ok - wouldn't really be my business. but since after we met physically we started a dating/courting period which led into a relationship which we both agree we want to be very serious, i dislike the fact that she's not empathic enough as to cut that person out.

firstly, i find out she lied about WHEN she had sex with him. before, she told me she'd met him a few months before me, i later found out she met him, but then had sex with him -after- me and her met physically. i said i can't change the past, but it's very uncomfortable for me to think that she'd want to still keep in contact with someone that she'd had sex with after me and her met. initially she said she didn't want a relationship when we met, but i said that we should have one. she agreed to it and is happy she did. however, i think out of respect for me, she shouldn't keep in contact with someone she had sex with -after- we met, given i think it cheapens the relationship, and makes me uncomfortable.

she then says that's 'controlling', or if she does it, she'd do it only because i tell her. isn't she acting egoistical or sociopathic in someway - or am i wrong in this?

Summarize the given text in a few sentences.
<bot>: girlfriend keeps in contact with guy she fucked after she met me and has the gall to lie about it and argue it with me like she didn't do anything wrong. showing sociopathic, egoistical and mean tendencies.