Her and her sister, what do I do?

Sooo, kinda sticky situation I've gotten myself into.

At the end of last year when me and my girlfriend broke up, and I jumped back into casual dating pretty quickly. I was just having no strings attached fun, partially to try and get over my ex(obviously). One of the girls that I saw consistently for about 2 months, decided not to see me anymore because we had known each other, through friends, for several months and she wanted a relationship that I wasn't ready for. She was a little upset and said she felt used(understandably so). Very sweet girl though and respectful of my feelings and situation which is why I want to try and return the favor...

It has been about 8 months since the last time we hung out and I just started seeing her older sister. It has only been a couple weeks, so this is still a casual relationship(but a sexual one) and sooner or later one of us is going to have to tell the younger sister. They are 5 years apart and aren't very close, and we briefly discussed telling her the other night with no definitive conclusion on what to do.

My question is who should tell her? When to tell her? The girl I'm seeing now doesn't want to tell her sister, at least not soon, but she said I am free to if I really want to, HELP!

No need to tell- yet. If it's casual and both parties still like the casual feeling of it.

Though I think when it gets more serious or goes of for another month or so the sister should be the one to tell. She has more obligation to her.

It would definately be weird, if not upsetting, if my sister had dated my ex. I wouldnt be mad about it, but it would be awkward. If the relationship remains casual, and nothing too serious, I see no reason to let her know about it.

I would expect my sister to tell me, not my ex. Just because, like girl68 said, there is more obligation there.

Regardless of who tells her, the relationship between the two sisters will never be the same again and will likely be permanently broken. This will most likely have a negative effect on relationship between you and your date's family should you decide to pursue things further with her.

Hope this will be a lesson learnt for you. Don't date the sisters of girls you dated before.

Wow, have fun with that. After this remember: don't double dip the same gene pool.

Mish laid it out, take it like a man.

I'm not her ex, we were never exclusive and she didn't tell her family about me either, so I'm good on that front. It was only two months and it wasn't much more serious than casual sex. She jetted when she realized I wasn't giving her much more than that anytime soon. She's also really cool, and not the type to hold a grudge so I don't think she'll really be upset. I can definitely see things getting serious between me and the girl I'm with now, and they have been lately, but we are both cautious about commitment. I just think her sister should hear it from one of us before someone else blind sides her with it.

You ****ed her and now your ****ing her sister. Same dick, different taco. There will be problems.