One of my sisters and I talk to each other about *everything* and are very close with each other. I accidentally found out she’s been “talking” to my baby daddy. When I found out, she just giggled, and later said “well I thought you didn’t want to be with him anyways?”. I don’t, but she’s the only person I’ve vented to about him. And now, they are both pretty much gaslighting me and acting like I have no reason at all to be upset. Ticked off.

Dear Ticked off, obviously she doesn't tell you "everything". If you don't want him, what's the problem? However, it's kind of skanky for your sister to do what she did. There's no way she didn't know it would bother you. What's the worst that could happen? Oh let's see, how about she has his baby, then both your kids would be half sibling/cousins!! Yikes! Let it go before it destroys the relationship between you and your sister if it hasn't already. At least she's not the only sister you have. As for baby daddy, CHILD SUPPORT PLEASE.