A very quick history, I came into my wife's life when she already had a daughter (6yo). Bio Dad ran away from finding out she was pregnant and has never been involved. I was the only man my wife let stay around long enough for SD to call dad and I am the only dad she has ever known. When she was 8 we had our middle boy and 10 we had our youngest boy.

SD always had an issue with lying mostly over silly things but is has been constant from fairly young. We thought she got over it when she went to university. She has also been quite 2 faced. There have been many times where she has taken a conversation she and I have had where we have joked about things mum does then twisted them when talking to her mum which has caused arguments between me and my wife. She has always struggled with friends, never had a great many and when they became close friends there would inevitably be a fall out and she would lose that friendship. Normally because she is quite bitchy behind people's backs. We have tried to help her with this.

I've always considered her "my" daughter. When my wife and I had no money my mum took SD on holiday and so did my brother. Even though I was the only one working she wanted for nothing. She went on all school trips and got the clothes etc she wanted. I paid for her to learn how to drive and I wanted her to live rent free while she went to University so she didn't end with loads of debt. I got her the brand new iPhone for her 21st. I'm not perfect and I made mistakes but she got all the love and support as though she was biologically mine.

In her final year at Uni she got with a new GF (her sexuality has never been an issue). Suddenly she dropped all her friends, family and paid little to no attention to her studies. She was always reluctant to bring new GF to meet her family and on the 2 occasions she did she made sure we couldn't get any real time to speak to new GF. Having spent no time with her own family from Oct to Christmas SD spent almost no time with us at Christmas too which caused an argument. My point being she should be able to exsit in her relationship and still have time for family. Both my wife and I were concerned because he behaviour had changed so much.

After her 1st set of exams, in Jan, SD had a meltdown, she had dropped her studies so much she wasn't prepared for her exams. So we had a conversation and I told her we would not be supporting her to become an amazing GF but we would support her to finish Uni so the choice was to continue to ignore Uni and start paying rent or limit time with new GF and focus on Uni for the last few months getting a good degree. She agreed to focus on  Uni.

SD then started coming home crying claiming that she had arguments with GF because GF wanted to see her all the time. She was describing new GF in very bad terms. GF spoke to her like crap in front of her friends and family and "as long as she controlled when she was her she was fine". SD told me that her friends had described GF as a "psycho" and she should dump her quickly. One night she sent messages to Mum and I saying she knew she couldn't stay over that night but she wanted to call us for us to say no. Stupidly I agreed. That night she came home crying saying it had caused a massive row and GF said she feels like she is in a relationship with a child. Really worried that she was entering into an abusive relationship, it caused a lot of stress at home and she began lying again. When she was claiming to be in the library she was with new GF. My wife was just as worried as me and even contacted new GF's ex because SD described so many red flags and her behaviour had totally changed. GF's ex described her as controlling and manipulative.

SD basically started to cut me out of her life. Started to ignore me when she was home, stopped messaging me and was being quite frosty. When I told my wife this she didn't want to get involved. So I took a step back and started to ignore SD. Hoping that she would see what she was doing and how it felt. When SD told my wife suddenly wife had a lot of opinions about it and it was all my fault. This continued for a few months until SD came home and announced she was moving out. She had said that GF was living with GF' brother and his wife and things were cramped and they felt uncomfortable there.

SD has a place on an advanced degree course and I was worried this would interfere with it. So my wife called her and wanted to speak to her about them both moving in with us so she could continue with her studies. Finally SD gave my wife attitude and wife saw what she was like so my wife said she needed to take a break from the situation. SD because very upset and new GF messaged my wife saying she was happy to take one for the team and tell SD she couldn't move in with her.

 I was instantly confused. That wasn't the action of someone who is controlling so we asked new GF to come round without SD because it had reached a ridiculous stage where SD had a totally seperate life. New GF is actually very nice and it's SD who has been very clingy and over reacted to GF wanting some space and has come home to us and told lies about what GF is like. The occasions where GF has spoken to her like crap were nothing of the sort and because SD is so clingy she has blown it out of proportion. Arguments that we were told had come from GF were actually SD lying so we would back down. GF was actually telling her to go home and see her family because she also needed space but SD would break down asking what she had done wrong.

She has at times cut me out of family times because I believed her lies and wanted to keep her safe. It's almost caused my wife and I to divorce because she blames me for all the tension. SD has reverted back to twisting things I've said to cause trouble. 

Now I've disengaged from SD. She has moved out but I don't feel like I can trust her or even have a conversation with her that isnt going to be twisted and cause my wife and I to break up. Wife thinks I'm at fault because of how I reacted and refuses to see what SD has done and just how messed up it is. We have gone from SD being "our daughter" to SD being my wife's daughter.

I'm not willing to get divorced over this and cause a broken home for our sons because when SD isn't on the scene things are good.

I feel a massive sense of loss but I just don't feel the same about SD as I did.

Is this normal for girls of her age and am I mental?