Apologies in advance as this may be quite long...
My sister has been in a relationship with a guy for 3 years. At the beginning she wasn't 100% sure about him and if he was her type but he was really over the top in showing how much he liked her (I've since seen people describe 'love-bombing' on here and it was pretty much that) and having been cheated on by her last boyfriend and treated pretty badly by him she took that as a good sign. To be honest so did my family and when she wasn't sure about him and asked what we thought of him we all thought he was great as he seemed to really be into her. I now know love-bombing is a huge red flag that we missed.
As they got more serious it wasn't long before we started to notice things that didn't seem quite right. He has been overheard by family members making comments putting her down like saying she looked better with her hair done differently or when she wore another dress when she was dressed up to go to a wedding. Around this time they began to have a lot of arguments and she clearly wasn't happy.
One night when she still lived with my parents my husband and I were staying the night and my parents were away for the weekend. I was woken up in the morning by her coming into our bed crying her eyes out. She said that her and her boyfriend had been out the night before and had been arguing, she came home and wanted to come alone but he refused to leave her and came back with her, forcing his way into the house behind her when she tried to close it over. She told him she didn't want him there but he came in anyway and she told me she hated that all night as she was crying in bed he lay beside her, holding onto her when she wanted him to leave. I really didn't like this and told her so, he should be respecting her space and her feelings and I thought it just wasn't right. The next day she told him she wasn't sure if they were working out and he told her his parents were splitting up and he was just having a stressful time, she stayed with him and his parents never split up.
He moved down to London temporarily for work and we kind of hoped that it would fizzle out with the distance but it didn't. Instead they have now bought a house together and he has moved back here. When they bought the house he went to see it with his parents and without her, he told her that this was 'the one' so when she went to see it she was pretty much going with the view that this was the one they were buying because (in her words) "this is the one he wants". Just before they closed on the house he started to say that he wasn't sure if it was the right one and that he was only buying it for her and that if it wasn't for her he wouldn't have moved back from London. She told him they didn't have to close but they went ahead with it. Once they got the keys she moved in but he didn't move in for 6 weeks, constantly giving different reasons why he couldn't. During this time my sister was living in an empty flat on her own. My family and I would go round and spend a lot of time with her and helped her to furnish and decorate. She was clearly really unhappy at this time but whenever we tried to talk to her about it she would become really defensive so we were careful with what we said as we didnt want to push her away. He eventually moved in and she started to seem a lot happier.
I went furniture shopping with them one day and when my sister saw something for the wall cost £60 she said she would love to buy it but would need to come back on pay day. He said he would pay and put it on 'her tab'. When I asked what this was my sister said that he kept a written record of anything she owed him. This turned out to include her half of meals and outings from the holidays that he had booked for her as gifts, money for their sofa (1/2 of the sofa was paid for by a member of my family as a gift, he paid for the other half but then said she owed him 1/4 of that), other items for their flat (if she liked it then basically she had to pay him back for it) and half of the cost of wedding gifts for his friends' weddings. Not long after he moved in her went away on holiday without her and he did a house swap with their house so that he could get free accommodation while he was away so my sister had to move out and into my parents during this time. He has also set up another house swap that she will need to move out for while he goes away at the start of next year.
The thing is that now my sister is constantly skint but he always has money, despite them both earning the same. She will literally say that she can't go out for dinner with their friends because she's skint, but he will go to the same dinner that she can't because he's not? I'm starting to really worry that he is using money as a means of controlling her. He has been on 8 holidays this year, 6 of them without her. They don't have a car but he bought a motorbike and so he will use that to go places but will say that she can't go because he's not comfortable taking her on the bike. Where she lives makes it difficult to travel to see our family now without a car so we make sure to drive to pick her up from there. When we suggested she get a car she said she would like one but he then said there's no reason for her to get one and she backed down.
My whole family are really worried about her. There are a list of other things that have happened that I won't even go into because I'd be here all night. In the past I have spoken to her and said that she deserves to be with someone who puts her first. She told him I'd said this and he didn't speak to me for a while but did start treating her much better for a bit so she would say everything was good again. But this seems to be the pattern- he acts like a dick, she gets to breaking point and threatens or tries to leave, he makes an excuse (parents splitting up, work is stressful, brother is ill, addicted to sleeping pills have all been excuses) then is all nice for a while until it gradually starts up again.
My parents aren't always the best at talking to her about their worries and she becomes immediately defensive and shuts them down. It's now starting to affect her relationship with them which is obviously exactly what her boyfriend wants.
I really don't know what we do now. Do we just need to accept what's going so that we can be there for her? Do we keep trying to talk to her (but in a better way)? The thing is that right now she seems to be in a 'happy stage' but we now are very used to the pattern. The thing that worries me the most right now is the things that he is doing in this 'happy stage' that previously would have upset or bothered her but now she just accepts. He is also incredibly charming so most people who meet him would say, 'he's a lovely guy' which seems a big thing for her as when she's been unhappy she's said to me in the past maybe it's her because everyone loves him. His ability to manipulate is really scary.
What's the best way for us to support her?
Sorry for the length.