No, you have not to blow your chances for getting rid of eric. But this is another route. You can give him the pills. On wednesday, when he is at moms room listen to a phone call, talk to kira, search on net about victor moro, talk again to kira, call hacker, but don't get him rid. And now, with this info, blackmail him as much as you can. give him the pills, but not on wednesdays, than you can enter mom's room during sex with eric and touch your mom. After thae last scene you can get rim rid be talking to hacker.
To get him rid via kate's mom, you have to wait until he wants to get his wallet/money, give him both (money and wallet) and then talk to kira, kate, kates mom, you need big weed and 5000, then you will get the sex video scene with alice.
You see, how you act after you have stolen the wallet, leads to different pathes.