Please help me :( :( :(?

My parents are divorced they have been since i was 1 so i cant remember them together. They both blame the divorce on each other. My mum married my step dad 7 years ago and for the whole marriage they have argued horribly and been separated and got back together, they argue in public a few times my step dad has driven off when we have been out for dinner and once we had to take a taxi home... My mum has recently started surfing and made a few guy friends.. I think one of them loves her hes really creepy and my sister step dad and i all don't like him. I don't know if mum likes him back in that way or not but my sister has read texts on my mums phone from him saying she has a y laugh and he loves her and stuff. Im scare they are having an affair im angry at my mum for it but i love her so much. My dad told my sister that he thinks my mum has a disorder where she gets angry and yeah but i dint think thats true i think she just has a bad temper lol. My mum and sister always argue and stuff my sister causes trouble a lot :S So my sister keeps staying at my dads house which really upsets me. I have been arguing with mum a bit but i hate it because we love her so much. mum says like that all my family hate her but we don't we all love her so much :( My pa used to keep my family together but he died in 05 and i keep crying about it :( I get really depressed about that stuff but mainly i get depressed about My body image so badly that i want to commit suicide.. My friend told me i probably have body dismorphic disorder (google it) which makes people want to commit suicide it is a mental problem...i have tried to be bulimic but i cant throw up i have like no gag reflex..i have been told that i ave a perfect body but i cant accept that i want to be super thin like a high fashion model. I feel like every one thinks im a loser and yeah.. I just hate my life.. Always think abut death and hurting myself but i dint do it... my dad is taking my sister to a psychologist and i have wanted to see a councilor for a long time but haven't wanted to worry anyone is there any other way i can get help and do You have any advice for the stuff i have said? And also do you think my mum and this guy are having an affair? thanks so much xx