Im hurting I need help urgently April!!

Hey,

Well I met this girl through the boyfriend at university but we only started out as friends and strictly nothing more. I knew he was completely wrong for her from the start, she was princess like and he was just to be brutally honest ugly and had a kinda control problem with her, he always had to bring her down by insulting her. To cut a long story short I realised he was treating her soooo bad and would call her horrible names in public including: whore, bitch etc… I couldnt believe what I was hearing. Shes from America and hes from the UK and she came all the way from USA to be with him in the UK so it is a hard situation for her as she kinda feels obliged to be with him as hes taken care of her for 3 years hes been with her etc…She began to flirt with me and even invited me round one night which I turned down twice as I just felt it was not appropriate as I still knew the BF and he was in my group at university which she valued really highly and knew i wasnt just after one thing. Anyway… as time went on I couldnt help but get close to her and she got close to me… and over easter she stayed at mine, (nothing happened at all) and I gave her a lift to the airport and she flew back to USA. By this stage she had made it clear that things with the BF were over. ALthough I am not the kind of guy to intrude on other peoples business, it was obvious she wanted it over. Over easter when she was back in USA we kept in contact every day and literally fell in love with each other. When she came back she had to live with the BF until summer and apparently he was threatening to not eat, sleep and was even contemplating slitting his wrists. She started ignoring me an became much more distant from me, and was just really hot and cold, which really really hurt and upset me as I was now in love with this girl. Summer came and things were still distant altho I met up with her and asked her why she was ignoring me. She said things were getting to complicated and she just didnt know what to do. Also she said she really likes the person who I am but felt I was far too easy to get wrapped up in and had to put the breaks on with such a difficult situation living with the BF or ex BF until the summer. She said she had finished with him and didnt see a future between the two of them. Also she even told me her mum asked her if she would think about having kids with him and she said that was disgusting. Finally she said she didnt want me to put all my eggs in one basket over the summer as she is coming back for herr final year next october which kinda upst me. One of my friends told me she told him she was thinking of living with the ex bf next year… which really hurt and upset me. I spoke to her today and she said online she loved talking to me and she will email me. I just dont know whether to wait or tell her exactly how I feel via email as I am frightened of her moving back in and losing her. If she moves back in with the BF next year then its all over. Everything is so perfect between us two, we are so compatible and over easter things were just soooo good, What shall i do!!!! I have devised a long deep email explaining how I feel and that if she moves back in with him, it will make me so upset and that she means the world to me etc….is this the right approach???? I actually love this girl and dont wanna lose her, help me April!