I can use some advice on relationships from anyone right now...!!!?

ok last night i was on the computer and my boyfriend was walking the dog and his baby moms told me i should write a letter to this girl brianna asking her if her and my boyfriend were together the baby moms said i deserved to know if he was playing me...so me i asked her and when jovon (my boyfriend) asked why i did it i told him the baby moms had told me to so now theres this whole arguement because shes saying she never told me to write anything to this girl so jovon got on briannas page and deleted my messages to her...what should i do? he thinks im keeping secrets and lying to him when im the one who should be worried if hes cheating or keeping secrets.....what should i do?...im trying to get the truth out but its really hard...