Welcome to HCM.
Your last LMP was 23-28 May and you did unprotected sex on first 3 days of JUNE.
Then you found out pregnant after relation breakup with your bf.
Your unprotected sex was prior to your exact ovulation time. If your period was regular,then your ovulation occurred around 6th to 9th June. Sperm can live 48 to 72 hrs inside uterus
and ovum can live 12-24hrs inside tube.So You probably conceived on 3rd June sex.
Consult with your doctor if you do not want this pregnancy
as early as possible.
Be well and avoid tension. Also practice safe sex