If I had pics of ex gfs and my new gf considered that distasteful or disrespectful or cheating, I would probably be inclined to agree to that boundary and get rid of them.
If, by chance I forgot there was something stashed in a shoebox and they found it, I could only say that when I got rid of things I didn’t remember that I had put any there.
My new partner would either have to believe that or not.
But once I explain and apologize, there isn’t much more I can do. And if my partner TRULY thinks I would lie to them and betray a boundary we agreed to on purpose, well maybe the relationship isn’t meant to be.
I would hope that isn’t the case. But I wouldn’t grovel either. And I would tell me partner that. They either think I’m the type of person to violate their boundaries and lie to them about it or they don’t. If this seems in character for me in their eyes, our connection is probably not that great.