Struggling with ex issues help! (it's kinda long sorry)

right so I'm an 18 year old male having some issues with a girl i once loved, its a pretty stretched out complicated situation so might take some typing but i'll try keep it simple. met a girl when we were at school aged i was aged 15/16ish got together had a very intense loving relationship for about 2 and a half years in which i loved and adored this girl as she did me (i think).. obviously our relationship wasnt without issues and arguments which mainly focused around my mental health issues and her disliking my drug use due to those issues... which is perfectly reasonable and we usually kissed and made up after these fights. it was when she mentioned a previous boyfriend she'd been with who suffered from similar mental issues (me psychosis him schizophrenia) and she would always tell me stories about how mysterious and the weird jesus like shit he did.. to put things into perspective a little i had a large belief i was living in some kind of fake reality.. like everything was a dream i was having and i was at some point going to wake in a hospital bed and find out id been hit by a car and been in a coma for 2 years.. i took a massive interest to this david guy regardless of the fact id never met him let alone seen a picture of the guy because i felt such a connection to the point where i felt as though he was a brother to me and i always used to try and get my girlfriend to arrange a meeting to no avail due to the fact she disliked him so much. i was crazy about him i wanted to meet him and talk about my mental issues and shit. what can i say i was in a bad way in my head. so anyway i feel a fool for not noticing this connection sooner but we watched a film called catfish one day if you havnt seen it its about this guy who makes friends with someone on facebook only a year later to find out everything about this person is a lie and its actually a completely different person posing as who they thought they were talking to.. you get the jist. so we've watched this film and like 3 weeks later my girlfriends all like 'ohh look this is that david guys profile on Facebook' so i go home and add him and no reply wait afew days search him again and there are two exact copies of the profile so i think he must not know how to use fb or whatever add him on the other one no reply for a week and then my girlfriend says "oh hey so david said he wants to speak to you heres his email address" i asked why and she just said she didnt know.. yet i was so messed in the head and desperate to talk to him i was not suspicious.. then began a series of emails that lasted the latter of the relationship between me and 'him' (emphasis on the inverted commas there) in which he would usually ask me how my relationship was going and telling me 'that girl could break you like a twig if she wanted' and this and that. so push finally came to shove and we broke up (me still not suspecting anything to do with emails) and i was devastated the rest of the year and using heavily and i finally got my act together sobered up and became mentally stable and i was looking over the emails and smelt a rat and the more i think about it the more holes start to appear in the woodwork.. like him telling me he was in the army and 'typing this email from the barracks' when i recently thought about joining and during research found anyone with a history of schizophrenia was permanently barred from being able too NO exceptions. i confronted her and she blamed the ideas i had on my paranoia and said i was being crazy and denied any involvement. i found i could trace the i.p of the emails which all traced back to have been sent from the same place and i can't say for certain that was the i.p of her computer but it did tell me that no email was sent from where 'david' was supposed to have been... hmm. (and you can say i was being obsessive but i was possibly about to find out about the biggest betrayal of my life so far and i wasnt about to just say never mind) so after more digging and confrontation she said she had got david to apparently come round and sit with her and email me about stuff because she was worried and thought id tell him things that i might keep from her. now she used to do this manipulative guilt trip thing when we were together that makes you feel like your the evil one when lying/ arguing and i new that she was lying but i could never get round it and in confrontation of the email shit she went into this little guilt mode and it made me realise just how much she probably lied to me when we were together.. so anyway a summary of the situation, im 99% sure it was all a sham and she was 'david' in the emails all along but theres always a chance i am wrong and her saying that im just being crazy and paranoid is actually a realistic idea but i fully need closure for this situation. its not about the love or the relationship or being bothered by the lies anymore although i am kinda pissed off haha. but i shit you not it is a very serious issue that the girl might think it ok to simply brush such a huge lie under the carpet by blaming it on my mental health being fucked up.. i mean heres me thinking i can get on with my life after getting over a rough patch but now i dont know whether im being overly paranoid and need to start seeing my psychiatrist again and taking some pretty nasty medication or im actually perfectly healthy and im just being lied to my face. its really distressing because every time i try to confront her she gets all defensive and says she wont speak to me if im just gonna "bring this up again" i need to try and communicate that i don't care whether she actually did it or not anymore i just want to know the truth so i can just get on with my life.. :( its a horrible feeling knowing i worked so hard to recover from these mental problems and now i dont know whether i even am better or not. please help! sorry that this is so long. ahh the difficulties with trying to confront a compulsive liar.