Hold on there, you forgot some steps.. Your brother need to catch you and Tamara making out at the vacation. Then you need to talk to the brother afterwards, and he want your help to set him up with Tamara. Then you need to speak to Tamara afaik, and then next time at vacation and you make out with Tamara, your bro come over. You need to repeat this a few times, before they do the dirty deed. Once that done, you need to talk with the brother and tamara again if I recall right. Then go to your brothers apartment and strip for him to start next chain of events.