How do I show love and acceptance to my sister (a Christian) who is sleeping with her boyfriend (not a Christian) and on the other hand show her that I don’t agree with her lifestyle?
First of all, I want to free you from the responsibility of having to change your sister’s actions. I understand that as her sister, you want the best for her, but the truth is that we only have as much influence in people’s lives as they have value for us. The best way you can impact your sister’s life would be to show her a love that she has never seen before. This unconditional love looks like you loving her the same no matter how she behaves, and it shows her that you love her for who she is, not what she does.
To live a virtuous lifestyle we need to have a vision, because having vision gives us strength to accomplish our goals. The virtues that we live by will guide our attitudes, which in turn, determine our choices, and it’s our choices that dictate our behavior. All this to say: it will be very hard for you to change your sister’s actions until she begins to have a value for purity.
My advice would be to not focus on your disagreements with your sister, but instead, to love her where she is. If she asks for your input or your advice then you can obviously be very honest with her but she needs to know that your love for her will not change.
You have the opportunity to send your sister a powerful message. As you continue to love her based on who she is, as opposed to what she does, your life will be a reflection of God’s unconditional love. It is from this place that you will be a great influence to her, which may result in her seeing your lifestyle and realizing she wants the same thing.
Here is a great website that talks about our love languages and how we feel most loved. It might be good for you to read through the 5 different languages and see which one your sister is. You can also take a quick test to find out yours: http://www.5lovelanguages.com/learn-the-languages/the-five-love-languages
Another resource is Sheri Silk’s message called “Insert Love Here”. You can get an audio download for $4 here: http://store.ibethel.org/p2740/insert-love-here
Here is an article that might also be helpful for you to read to maybe understand your sister’s struggle a little better: http://www.experiencinghope.org/sexual-integrity