I have a queation about a tmoblie g1 phoneeee!?!!?!?

I have a tmblie g1..and I have a txting problem...for some reason my phone isn't txting my bfs number...but we were able to txt lastnight around 10:45...and a few mins ago we tryed txting again but for some reason it won't go threw...I'm able to recive his txtmesaages but he cnt recive mine but t says it sent??...I can txt other people and they get my massage...is there a setting or somethingg?? Plz help ASAP!!!!!