There are some 'rules' in a couple that are silently established regarding the past. Does the past remain the past, or will it matter in your present? Is it a cause for jealousy situations? Have there been similar conversations before?
Every girl basically knows how her partner will react!
Also, I think it's worth asking yourself why you feel guilty and why you feel the urge to tell him something from the past. There's no reason to feel bad about your previous relationship or relationships. Even if you occasionally feel a nostalgic longing for an ex. That's normal.
Personally, I don't necessarily want to know about every person my boyfriend has had a relationship with.
If you tell him...
He might get angry.
If you think he won't handle the events of your past life well—being sullen and moody all night, questioning your actions and motives—then you absolutely shouldn't tell him. You've already agreed not to talk about it, so please don't feel guilty about holding back.
Sometimes not sharing information isn't about hiding a bad truth, but understanding that the information isn't necessarily helpful to your partner.
There's no one-size-fits-all answer here. Do your best considering what situation you're in, how your partner might react, and what the spirit of the original agreement was.
Would this information make your relationship better or easier? Or is it just trivial gossip that will just sting? You don't deserve to feel guilty about previous relationships (even casual ones), nor should you feel the need to keep unpleasant secrets.
