Relationships

Can you help me understand why my boyfriend doesn't want to re-add me on facebook?

Me and my boyfriend have been together for two years (most of which we lived together). A couple weeks ago we broke up because we'd been arguing a lot and he'd just had enough and moved out of our home. A couple hours later he deleted me from his facebook and also blocked me. A friend informed me though that he'd added a couple girls who have in the past flirted and hit on him. One of whom was his ex. Within 24 hours of the breakup though we were talking (and sleeping together) again. A week later he asked if he could move back home because he missed me. We talked about the week we were broken up and he confessed that he'd been talking to his ex a lot and had even discussed getting back together (she is also the mother of his child), but that he'd decided that he wants to be with me. So far things have been going pretty good between us. The thing that concerns me is why he won't re-add me on Facebook. He did tell me that he'd deleted almost 50 people off of it after we got back together, but he hasn't deleted his ex. He says it's because she's always posting pictures of his daughter on her site, and he likes that access. When I asked him why he didn't want to add me he said that it would only cause drama (his ex HATES me and has tried repeatedly to break us up). I'm trying very hard to remember that he's living with me, he says he wants to be with me, and that Facebook does not define our relationship. It does admittedly bother me though because I feel like he's hiding the fact that we're back together. I don't feel like he's cheating on me, but I don't think he realizes or cares that it makes me feel like he's hiding something from me. Can you please enlighten me so that I can stop over-thinking it?
Updates
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Alright, I suppose I should post an update. We're still not friends on Facebook but I don't even care anymore. He has given me full access to his account. He leaves himself logged in on his computer, his phone is unlocked and it's a smart phone so I could go to his page from there, plus he's even told me his password so I could even log onto his page from my computer. Honestly, I haven't checked his page once though, he's went to great lengths to prove to me that he's being honest.
Updates
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I've decided to try this thing called trust. Not only all that but we also have mutual friends who would tell me if he was doing something wrong and his relationship status is set to "in a relationship". I'm not even sweating it anymore. Thanks for your answers though.
Updates
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Oh, one last thing. He deleted his ex a couple months ago. He said they couldn't be friends, and it was also causing drama.
Can you help me understand why my boyfriend doesn't want to re-add me on facebook?
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