I am not making any judgments here, just need a little more info, that's all. If she is prone to drinking now and then, or having a smoke, then she probably was bored and was playing around with you.
If she is 'straight', then she still is playing a game with you, and gets encouragement from her cousin.
If you are over this relationship (which I hope you are) then maintain a steady life, getting to meet new people and enjoying life in general.
Don't worry about her or give her any second thoughts, as it's difficult enough trying to figure someone out. Plus, I'm sure that after six months, you are on the road to heal and I suggest you stay on that road and let her live her life with her games. Don't try to figure her out, it's not rational for her to act this way and I would avoid her if at all possible.
Life is too short to re-hash pain and rejection so go and find someone who appreciates you for yourself and will not play stupid games. She needs to grow up, and you need to realize that you can't help her in that - it's on her.
The right gal will show up for you and you will have fun, enjoy being together without trying to figure her out first. A serious relationship should not be based on what this gal is doing.
Wishing you lots of luck and stamina - and please keep us posted.
Games are for Kindergarten kids - you don't need them anymore.