imintrouble you poor thing, I can't believe this has happened to you after everything that's happened in your past too. To anyone else reading, don't judge too harshly, this lady has been through a lot.
Of course I don't think badly of you! I'm your friend you didn't mean for it to happen. You're a great mother, but you're also young and god knows we all want to get smashed out of our brains and forget about our day now and then, and you've had such a hard time lately, I'm not surprised you wanted to feel as un-motherlike as possible for one night only (if that makes sense)
Personally I think you're taking on too much responsibility for this. If you were out of it, he shouldn't have slept with you. I know you don't want a fuss but personally I think he did take advantage of you. It's a decision you need to make for yourself but don't feel too guilty, love, I don't believe for a second it was all your fault or that you invited it to happen. But anyway, enough of that part of it.
Have you done a test yet? If not you need to do one asap as you might not be pregnant at all, and this situation won't be as bad as you first thought. Try to do one today if possible, I know it'll be hard but text me if I can be of any help, if only a virtual hand to hold.
Again, so sorry this has happened, you really really didn't deserve this.