Dear R.:
I am 45, mother of 2 grown up married girls and 2 pre-schoolers. I was a single mom most of my life, and like you raised 2 girls most of the time on my own. My best wish for you is to dedicate your life, children, home to God, finding guidance and strength in Jesus. Raising teenagers can be tough on anyone, we can't do it by ourselves!
I understand your situation with one of your girls! I tried to be a friend to my girls yet there were times they didn't say the truth to avoid getting punish or to avoid hurting me and disappoint me. I can't tell you how many times I cried not knowing what to do next, what to say! One of my girls got pregnant when she was turning 17. Because she was so irregular, I didn't learn she was pregnant until she was 5 months pregnant. I felt so heart broken because she didn't trust me enough to let me help her. She took medications and went into early labor. The doctors couldn't help the baby, and the same day the baby was born, she died... You can share this story with your girls, no matter how hard might be to say the truth, mom will always be there to love you and hug you, no matter how big a problem is. Boyfriends might come and go, even husbands, but the bond between a mother and her daughters is a very special one...
My oldest one while in college, had a boyfriend, they were living together. He had an accident lifting weights and after a difficult surgery, didn't last too long and died. My daughter was devastated but we, (I was remarried by then) supported her the best we could.
Now a days both "girls" are in their mid-late tweenties, married both. They married with good guys, thank God. but it has been a tough journey... Many hugs to you, feel free to email me if you wish. I know how lonely, how hard can it be but it doesn't have to be like that!
From my heart,
R.