You're not going to be able to do it in a way that doesn't hurt his feelings. Just be completely, totally honest. Tell him exactly why you're breaking up with him so he knows and can work on whatever he was doing wrong for the next relationship he gets into. Even if it's not something he can change, he deserves to know the truth instead of some sugar coated break up line.
You could go to them to their face and say i dont think this is working. My boyfriend got mad and stuff when i texted him it or got someone els to do it. Or give him an note. Just make sure you two are alone and just say it.