How can I get him back?

I don't know how to fix this situation. I was with my boyfriend when 2 male friends who have a crush on me wrote me on Facebook.
I've known them since before my current relationship.
Guy #1 asked why I would not respond to him.
Guy #2 asked if i would be his Valentine.
I told both these guys previously I'm in a relationship in the past and it's been months since I've spoken to either of them.
I responded to guy #1 by saying "don't you have a girlfriend"?
And guy #2 by saying "you probably write this to all the girls on FB".
I said that out of annoyance for them constantly contacting me.
My boyfriend saw these messages and broke up with me. He said he can't trust me anymore and he doesn't wanna drag me through his trust issues.
But he also said he loves me and he just doesn't know how to fix this situation so we need a break.
He thinks i was wrong for responding to the messages and not firmly telling those guys to back off.
I agree with him, i know i could of responded better to those messages. I made a big mistake and i apologized and asked to gain trust back slowly.
He said i can't gain his trust because i already messed up and i can't redo the past. We have been together for three years we never have arguments and I've never cheated on him.

I can't understand how he can throw all that away over FB messages where i didn't say anything outrageous