I'm sure if your bf is in a relationship with you right now, he
is devoted to you wholeheartedly. He might still have feelings for
his ex, especially if it were his first love, but it's over and he
knows it. I keep pictures of my first gf too, as what we had is a
part of me that I never want erased. That doesn't mean I won't love
my future gf wholeheartedly, heck, I'll even learn to treasure her
more.
Trust your bf, give him the benefit of the doubt, he'll love you
more for understanding.