Has your dh been AWOL or inexplicably late home? Does he have a job that provides time or opportunity for him to play away?
Is it possible that what you've seen is the equivalent of 'phone sex' rather than evidence of actual infidelity/adultery?
Bearing in mind your forthcoming holiday with your parents, are you a passable actress and do you have the cunning self-restraint to say nothing at the present time?
If you confront your dh now, regardless of whether he denies or confesses, the fall-out will cast a pall over your holiday. In addition, your parents will inevitably pick up on any tension between the two of you and, trust me, the last thing you need is for others no matter how caring or well-meaning to get involved at this stage.
If you can visualise placing what you read on your dh's phone into a box, closing the lid, and putting a sticker on it saying 'to be opened at a later date', you may be able to proceed with your holiday as if nothing has happened and with the knowledge that, if there is an OW, he is not with her.
With your parents around to lend a hand, you may be able to find time to perhaps slope off for dinner/drinks with your dh, rekindle the intimacy and subtly remind him of all that he has with you and his dc, and what he's been missing.
If he has been having an affair of some kind, the sight of you guilelessly delighting in his company, giving him adoring glances, bigging him up in front your parents even though you feel like stringing the bastard up will guilt-trip him big time although, being male, he's unlikely to show it.
Of course you should keep an eye out to see if your dh appears to be fixated by his mobile or continually finds excuses to 'pop out' on his own, but always remember that holding your tongue is not a sign of weakness and that honey attracts more flies than vinegar.
I know wise women who've pulled this off - their ohs have no idea that they were hauled back from the brink by clever and determined wives who weren't going to give OW the satisfaction of causing marital disharmony and walking off with their dhs.
One of these amazing women saw off the opposition by enslaving her dh all over again, then told him exactly what she thought of him and filed for divorce - the ink is dry on the Absolute and he's still begging for a reconciliation.
Unknown to him, she adores him and remarriage is on the cards once she's convinced that he'll cut his dick off rather than do the dirty on her again.
You say 'I really don't want our marriage to end'. I say 'there's no reason why it should'.