*hug* it's okay, we're here for you!!
The medical abortion is very safe. There are normally 2 pills (believe) that you will end up taking: one at the clinic and one later on. The time it takes for your body to start basically miscarrying will depend on your body type, and this specific pregnancy. There can be moderate to severe period-like cramping, but it won't last the whole time. Basic pain killers can deal with it, like pamprin or motrin or your regular period-pain medication, if you have one.
The consequence is that... You won't be pregnant anymore :) I know it is a very tough desicion though!! It is very scary, but you can always come to us for advice and support! You'll be okay!
We are here to support your desicion, and i'm glad that you are still keeping control of your life and making this desicion for yourself and your future. You can tell your boyfriend if you wish too, but seeing as you're breaking up with him anyway - and he sounds like a sleaze ;) - it's up to you.