I am 18 weeks and 1 day pregnant today. My due date is october 9th.

My boyfriend and I got in a huge fight in january and I ended up cheating on him (god I feel like the worst person in the world for it.)
my lmp started january 2nd ended january 6th than I bled for another day after.
Had sex with other guy january 6th
had sex with boyfriend january 15th
my cycles are usually 26 to 28 days never anymore or anyless.
I had an ultrasound at 7 weeks pregnant a regular ultra sound and vaginal one. The lady said I concieved january 16th give or take a day.

Please tell me can I relax and know this is my boyfriends baby or is my life ruined because of my infidelity. I am almost in tears right now, I am so scared.