Keep the dog.
Most fears are based, IMO, of being unable to predict or understand dog body language and communication. Thinking small=safe and larger=killing machine suggests that your boyfriend doesn't actually know what a dog is thinking when their ears are pricked up and forward but still relaxed, the various sounds they make that aren't growls but general talking - can he even identify the 'play with me' dip?
DP grew up with working dogs around where he lived - so the most interaction he had was of one protecting their home. But we would sit on the beach and watch the dogs playing, investigating, saying to anybody who knew to look OHMIGODTHISISAMAZEBALLS, BIRD!BIRD!WATER!BIRD!SEAWEED!COLD!, what on earth is that? Muuuuuuum?, MUUUUUUUMLOOKI'MRUNNING, or my favourite YAYYAYYAYYAYI'MONABEACHANDTHERE'SPEOPLEWHYHELLOPEOPLESITTINGTHEREDOYOUHAVEBISCUITSINYOURBAGNICETOMEETYOUIMOFFTOSEEIFANYBODYELSEHASBISCUITSYAYYAYYAYILOVETHEBEACH.
It didn't take him long to learn what they looked like when happy, unsure, excited - all of which a frightened person is unlikely to be able to discern, especially with talkative dogs like Staffies, as a lot of their grumbles, moans and witterings sound like growls to the unknowing. the fact they have heads like breezeblocks and no effective braking system doesn't help. He's now happy when the monster staffie/black lab down the road insists upon having fusses from me whenever he sees me and has fussed him himself when it's decided well, the man's with the friendly lady so I'll say hello for a bit (he's a bit of a jumper, but he's learning to try and keep at least three paws on the ground). And he's said he would like us to get a puppy when the time is right.
DP knew I loved animals and, having seen how the DTwatCats behave (again, he had outdoor/farm cats, not 'pet' cats), he decided that he needed to understand why/how I deal with them. He made the effort, despite his upbringing telling him that dogs were dangerous, cats were scratchy and so on.
Had he not made that effort, he would still be scared all the time. And not with me.
I would never abandon animals that were dependent upon me, that I have a lifelong responsibility towards, just to make somebody else feel more important.