How long have you been together? Early-late 20s? Are you both living together at your house with parents? Are you both using? If you are, that's okay... Contrary to popular belief and scary fundie religious types, opiates/opioids on the whole do NOT cause birth defects! I have birthed two incredibly beautiful children (my infant is doing ads for a major retailer right now [not my idea] and my toddler is incredibly advanced in all ways) while on pills both pregnancies. First pregnancy I had a fairly high hydrocodone script from same OB as 2nd; except hydro was schedule 3 during my first pregnancy, and became 2 right before my second...
During my second pregnancy, I'm ashamed to admit that I did not take them always under supervision of a doctor. That is to say he knew, but not how many. I was up to 35mg a day with my script and shit I bought (1/2-1 blue M box ir/day, broken into several pieces every couple hours, eaten) because my scripts while pregnant were measly for me (40 5mg hydrocodone per month) but probably considered high by anyone who does not understand pregnancy and chronic pain. I guess long story short; my doctor knew I was on opioids, just not how much exactly, and the ONLY thing we worried about was the very SLIGHT chance of neonatal abstinence syndrome otherwise known as withdrawal in the baby, which the baby had none of as I quit two weeks before delivery.
Anyway, I know I'm probably going to get another weird ass lurker following me and downvoting all of my posts for admitting to this, but I don't care. If it helps you feel safer knowing the baby is safe, then it's worth it. Two girlfriends of mine also delivered on methadone after both being IV H addicts, and their babies are now perfect school-age kids.
I don't know how long you plan to be together, but if it's forever (for what you feel is the "sake of the child" or whatever reason) then honesty and communication will have to come first before everything else in order for it to ever work. Along, of course, with patience, understanding, empathy... I'm sure you know all of this, but from a woman's point-of-view, being pregnant can be a really scary fucking thing, especially if not planned or wanted, and can lead women to doing things that they would never otherwise do.
I hope everything works out for you both. All my love.