I too have issues with cutting and also bad tattoos from my "try hard" period and on boy mode I always wore long sleeves to hide my numerous scars and cheap, horrid tattoos. Slowly I am now building my feminine wardrobe and finding great long sleeve pieces to wear. I'd say it would be okay to always wear long sleeves for you. Keen to this issue, I have looked around at other women and even in the depths of the hot mid-Atlantic USA summer I have seen quite a few wearing long sleeves. Not most people, but enough to where you wouldn't draw attention. Of course it can limit your clothing choices, but if it's the summer months I do not believe you'll necessarily look out of place or anything. Rock those long sleeves, be confident and you'll be okay.