Hi Florge
I understand your bf point of view. You probably have more hair raising experiences in Manila than he realises. But it is the fact you do not know which particular areas are unsafe,would concern him.Small time crime is problem in Britain.
Don't be alone at night time. Usual common sense stuff. Don't carry anything around that is visible to thieves-makes you a target for mugging. Things such as expensive mobile phones or IPods. City can have drug problems and opportune thieves will nick a phone or your bag for a quick sell for their drug fix.
I would assume the city is as safe as most. Forum members from Manchester will be able to tell you of places to avoid at night. I only visited.
But Manchester is easy to get around on foot, and the Metrolink tramway is there too. Go visit Piccadilly Gardens.
How about going to a Manchester Utd game? They are one of the biggest clubs in football these days. I am sure it would be an enjoyable experience. I would love to go there.