Well first and foremost sair, it would of been nice from you to respond to AB's advice from your question posted 8 odd hours ago.
In regards to your boyfriend, i can only agree with other AB's, you have to confront him yourself, it might be difficult for you, but you really do need piece of mind, imagine if your reliable source has got the wrong end of the stick, it will look very silly you dumping him then would'nt it.
The other thing is, what is it these days with dumping someone by txt ?it seems to be a common occurence with people, its insincere, nasty & weak, i really do wish that people confront these type of issue's rather than go down the txt route.
And if it is true he has cheated on you, its game over, once a cheat always a cheat, i'm sure someone will tell you about 2nd chances giving etc, but once the trust issue has been broken in your mind, its extremely difficult to get that trust back with that person who cheated on you.
Good luck