my partner (20nb) cheated on me (18nb) and im so lost.

i truly just don't even know how to react about it, it was in september of last year and i only found out last week from doing some snooping, i only found out 2 months away from our 3 year anniversary.

they said they were sorry , and it wasn't anything more than talking and it only lasted a week but i just find it so hard to trust... i want to forgive them and i want to trust that he will do better. they said they would do better and do whatever i needed to rebuild my trust and love but it's so hard to believe... i told them i need a break for 2 weeks-a month because i need space to think and they agreed, but im so lost on what to do! i need help!