partners parents are EVIL help!!?

Me and my partner have been together for 7 years nearly and I don't think I can cope any more. We live with his parents and at first when I moved in everything was fine until they started to show their true colours. They always seem to have no money and always rely on us to give them money, I had to buy them an £800 cooker out of my catalogue as theirs had broke which I had no problem with at first as they offered to pay me every month for it, which never happened because after the first month they reckoned they couldn't afford it so I had to foot the bill of £60 per month to pay it as other wise I would have ended up in debt. Then the shower broke, so of course the same thing happened again and as they have got me over a barrel, I have to pay it. I then paid £500 of mortgage arrears off for them along with other bits and pieces that all amounted to around £1000 when I got some inheritance money for my last birthday as a gesture to help them out. However despite all this and countless other things I have bought and helped them with they seem to think I'm just some c*nt. They slag me off to my boyfriend, and when we have an argument it can never be just between us two it involves them every single time because they stick the knife in and cleverly tell my bf what he wabts to hear, they gather ammunition over the weeks such as hw long I had left my things in the tumble dryer, and when I didn't buy milk and bring it all up when we argue which of course riles my partner even more and we have an even bigger argument. The biggest blow came however, when they used my ebay account to buy something, looked on their bank statements to see something had gone out for ebay at £13, allegedly "forgot" they bought something, and when our next argument came, told my boyfriend that I was a theif and I had stolen the money to buy something on ebay and hoped they wouldn't notice!!! And of course because my bf was already p*ssed at me decided to have a go at me, I just couldn't believe it. I am not close to any of my family and don't really have anyone to talk to about my troubles and I feel so alone sometimes because I have no one for advice. Do you think that our 7 year relationship is worth holding on to when this is always happening? I am trying do hard to move out but me and my partner just simply can't afford it but I don't know if I can cope any more. If we split up this is exactly what his parents want....