Substitute

went to my boyfriend's place the other day because he needed me to pick up something, I was meant to find a piece of paper, so i went to his drawers and there was a piece of paper, so i assumed it might be it, i opened it and it was just some random text that i immediately ignored because i needed to find a number. but the odd thing was that right beneath it is a photo of him and his ex-girlfriend in a photo booth and behind it, it says: the best part about me, is you". I'm not angry nor do i want to start a fight because he's already going through a difficult situation, although he keeps telling me he's fine. but i can't help but to wonder why he's still keeping it, this isn't like it slipped out of an old box, and i wasn't even snooping around, it was just placed there. and i also understand that we all have people that we miss in our pass, and maybe he does miss her, which i won't blame him as it's a natural emotion. but what does that mean to me? Am i a substitute to a residual relationship? Is everything he's been saying about her a lie? Are they still in contact, even though he said he never wants to speak to her again? If soul mates do exist, it makes me question if they really were soul mates, despite all their differences, the lies, the hurt, the cheating. maybe I am a temporary substitute, with an easier geographical access. I'm not sure if there's a point in bringing this up, because I know that the response is going to be that I misunderstood and he doesn't have feelings for her. We've been really good for a while, I hope this doesn't shake things up between us. I've been trying to masturbate these days, but I keep seeing that image in my head, and i've been cool around him when he keeps trying to talk about sex, but I find it hard to say: oh i'm so horny but I don't wanna talk about it with you, because I keep remembering the good sex you've had with your ex and how she took out a condom from her panties to seduce you and you found it super hot. or that when you first got together, you eskimo kissed, just like you did with me when you first met me, or that i think she kinda looks like me, with the tiny body, light skin and long brown hair. Substitute? copycat? Ugh, I dunno. Just when I started feeling comfortable with my sexuality, this happens. I'm never gonna have full on sex when this sheet keeps happening, for a moment i thought we might take this step, although I've been telling myself not to coz it might sound like something simple now, but it might hold a significance when it actually happens and i freak out, or that he thinks the same way, i guess i'm glad this happened so that it would be a wake up call to not consider penetration for another year.
You are replaceable, whether you like it or not. your first time should be with someone that finds you irreplaceable.
I should try and let it go, I don't want us arguing, I just hope this doesn't fuck up our sex life completely.