Hi,
I'm new here too.
I used to be the same as you... I started with compulsive lying when I was 17 and met a guy. He was 23 and I fell for him hook, line and sinker. My relationship lasted, on and off, for 12 years. I was abused by him physically, mentally, emotionally and sexually. I lied to cover for him and eventually I was just lying about everything and anything.
He knew I was lying and I would get a slap for it. We split up 3 years ago. I took a vow of brutal honesty and, no matter what the consequences, I said what I was thinking and I didn't sugar coat things either. I totally removed the brain to mouth filter. It took people a long time to start trusting me again but now I am the one of the only people that they can trust to be honest with them.
It wasn't easy to break the habit but I found a way to do it. I got one of those sealed money tins which you need a can opener to get in to. Every time I lied, I had to put £10 in there. I wasn't working at the time so £10 was a lot for me to lose when I had next to nothing. I gave the tin to my housemate so I couldn't have access to it but I was honest each time I lied and put the money in.
Maybe you could try something like that.