Making out with your sister is wrong, and you should stop doing it immediately without looking for reasons other than my telling you to stop. You don’t need to know how to stop it — you already do. Just don’t. Quit it now.
Your reasons for doing it probably have to do with an inappropriate (at best) and severely abusive (at worst) family background. You can do the history homework and analysis on your own time. For now, stop hurting yourself and your sister by not acting inappropriately, and by looking for new, healthy friends so you can break out of whatever social circles and family patterns you’ve been in that have, in one way or another, led you to this behavior.