Well, chances are that while he was performing manual sex on you, he might have made one or more small tears in your vaginal tissue. The bleeding should probably stop fairly quickly, but you'll have to watch out for vaginal infections now since he might have had bacteria or something under his nails. You should definately see a doctor if the bleeding continues. There's a really easy way to prevent this. Have him wear latex gloves while performing manual sex, and add in some nice water-based, condom-safe lube (like Astroglide or KY). It feels good, and lets you not have to worry about getting nasty infections. Get yourself and your boyfriend tested for STD's while you're at it, that's always a good idea if you're going to have sexual contact at all!
And just as a note, if you'll check the guidlines you agreed to when you signed up here...
quote:
When posting, you are expected to be respectful of your fellow posters and our staff, and to use language which is unlikely to offend anyone, which is not salacious or overly explicit, and which encourages intelligent, safe and mature discussion of the issues at hand. We ask that you post with care to grammar and punctuation, so that it is easiest for everyone to understand you, and easiest for users to search for subjects. You may not post multiple identical or similar topics in different threads, and you may not use more than one handle for posting.
It's not necessary to post this both here and in Ask A Sexpert. This just helps us keep the confusion down. Thanks! 
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~KittenGoddess
Scarleteen Advocate
"Not everything in this magical world is quite what it seems"
"Remember, I'm pullin' for ya. We're all in this together!"
[This message has been edited by KittenGoddess (edited 10-23-2001).]