Given that you began your relationship with your husband so young, neither of you had experienced other relationships. So you got pretty emeshed in each other unknowingly. We grow through experiencing different relationships, we learn and grow as a person. From what you descibed you did not experience enough life lessons from experiencing different relationships and as a result you did not learn more about boundaries.

Then the two of you being bored which can happen invited a stranger in for both of you and all it did was create a huge mess for both of you. Your husband doesn't have boundaries with this woman and neither did you and this woman used both of you and she has problems herself. So it's as though there really was no adult and more mature presence in the mess.

No one has any boundaries, it's just a mish mash of who is more lost.

Also, your husband is escaping through drugs and that makes an already bad situation worse. This woman has been a very bad influence. You need to cut them loose and get your own life together. And see a therapist that can help you with that. You really need to get out of this toxic triangle for your own mental health.