Search Results: falling for best friend

OK, I'm 26 and my little sister is 23 years old and she lives in the appartment with me. When she was 6 and I was 9, our mom died and our dad (who was a mysogynistic asshole) started drinking heavily and he physically beat her on a regular basis up until she was about 12 years old. I rember after he beat her she would always come to me for consolance and I would hold her and soothe her to sleep. Don't get me wrong, my sister is an incredibly sweet and caring person, but 6 years of continous abuse took a heavy toll, left her with severe PTSD and stunted her emotional growth (right now she has about the level of emotional development as a 9 year old). When she was 18, she moved in with me at my appartment and she's like my best friend in the world and because of her PTSD, she's an extremely affectionate person. Whenever we see each other after work she gets a long hug, she snuggles up next to me and we share a bed and cuddle together each night. We talk for a bit and I usually play with her hair or rub her back to put her to sleep. Because of her PTSD she has trouble falling asleep alone and even if she does she has nightmates. I know some people might find the thought of cuddling a sibling weird but I don't. Now I never got aroused but I think it's nice and relaxing to hold a warm person who you know loves you more than anything next to you. And when she's asleep and I'm holding her she looks so sweet and innocent and it makes my heart melt. But latley I started seeing this girl and as our relationship started to get more serious, I encouraged my sister to go to counseling and she did and she started taking anxiety medications. But my girlfriend said that if she's going to stay in a relationship with me, I have to tone down the affection levels with my sister. I told her that I plan on it but these things can't be fixed overnight, but she says I have to stop now or else she'll break up with me, what should I do?