Ok...first....BREATHE!!! Bless you, I've been right where you are right now..and I know it's overwhelming...hell it's overwhelming just reading what you've been thru/are going thru. (hugsss)
YES, I think therapy would be appropriate. You should not have to do this alone, and even tho you think you're fine working thru it, there are so many tools that a T can give you that you don't know of yet. Not to mention, working thru past issues that you haven't even addressed yet, even as you think you have. Remembering stuff that happened when you were a child is NOT the same as managing how it made you feel, understanding the hurt, fear, depression it left you with.
First things first....I'm not sure in your state (country) if you need to be referred by a psychiatrist but if so, make an appointment asap. Get an official dx....THEN worry about what to tell your parents/husband/family. In fact, once you enter therapy, your T can help explain this disorder with you to your family, if you think it would help....and in my opinion, it will....it helped me with my family.
Don't worry about costs or frequency of visit UNTIL you get your dx and UNTIL you speak to your T the first time. He or she can advise a schedule that will help without breaking the bank ... most T's are very accomodating, if they see you are serious about trying to get better.
Don't worry about the adoption issue right now, either, darlin. That is in the future; again a T can help you with this issue (understanding the ramifications etc). Right now...and I can't say this clearly enough....YOU NEED TO TAKE CARE OF YOU....for yourself, your child, and your husband. Everything else can wait.
Not you. You've waited long enough. Do this for you, but do it with help. People who suffer with BPD spend too much of their lives fighting dragons and demons alone....when we can get help, we often feel we're not worthy enough or our issues are not important enough. That's the disorder talking. It's not true.
You are important and worthy and you need help to help you. And there is help to be had, so please please do this for you. You'll be glad you did.
The relief of having someone to understand and guide you, is almost as overwhelming as the realization of BPD...but in so much a better way.
Take care