I met this guy few weeks ago, when I went to visit

I met this guy few weeks ago, when I went to visit my brother, he picked interest in me, and came to tell me about it, he told me he really likes me so much, that he want to be my friend at first, we became friends and started talking on phone, within a short period, we became so close, that I even started having feelings for him too, and he asked me to be his girlfriend, which I accepted without even wasting any time at all, we were both in love with each other, I could really see it and his eyes that he loves me, and I felt the same way too,
Few days after we started dating, I found out that he was in a relationship with another girl even before me. Ofcourse I was really sad, but I had already love him so much already to get really mad(ofcourse I was mad) so I asked him what it gonna be, because if there is something I really don’t like doing is sharing my boyfriend, but in this case, I think am the intruder… I thought I could turn a blind eyes to it and just let love lead, but it keeps coming back to my head that am sharing him with someone else. So I decided to take a step in solving it(so I thought), I asked him to choose who he wanted to be with, so he could drop the other person.
And I made it very clear to him that if he really love her, that I was willing to step back for her, because after all, she was there before me,…….he said that it was very difficult, that he really loves me, and wouldn’t want to loose me, at the same time, he wouldn’t want to just dump the other girl just like that,he feels it will be very unfair, and I understand that, but still, am not okay with the fact that am either a side chick or dating someone’s boyfriend or the fact that my boyfriend has two girlfriends ( it breaks my heart to think of it like that).
I have tried to live like that, predenting its okay, but it’s still in my chest, and it’s really bother me.
I decided to bring it up again today with him, to tell him that am still not okay with it, and that he has to make a choice 🤷
And what he said really got to me, and have really got me thinking, and now, I can’t sleep…..
He said”have you ever thought of how she is feeling now, that she called him yesterday and was complaining that he doesn’t call her like he use to and that scares her, that she doesn’t want to loose him” 😧 now I feel really sad for her, because I feel, I have come in between a relationship and she is feeling sad because of me, and it really hurt me,😢 really it does, but I really do love him too, and I don’t want to loose him😩😩😩
So pls I really need your help and advice pls🙏
What should I do pls?? Should I step down?? Or still pressurized him to choose?? Pls help me🙏🙏😩😩😩