Well, as baptized catechumen myself, this is my view on the situation:
There are two types of sins: tolerable sins, and intolerable sins. Intolerable sins are the ones we have laws against. These are all of our sins that have direct consequences on other people. For example: theft, murder, assault.
Then there are tolerable sins. These are things which are immoral, often gravely so, but because they only directly affect the people directly involved in committing them, they are tolerated by society. For example: cigarettes, alcoholism*, sexual immorality between consenting adults.
- Abuse and neglect caused by alcoholism are sins that directly affectly other people, whereas alcoholism only directly affects yourself.
I’m pro-choice on a lot of things - drugs and sex are big ones. I think that anything other than procreative intercourse within the context of monogamous, heterosexual marriage is gravely immoral. I think that self-abuse of ones body with foreign substances is gravely immoral - but I do not think that these sins are worth regulating. I think that because they only directly affect those committing the sin, they should be tolerated.
Of course, what we are to do when loved ones start committing tolerable is a much more complex issue. We care very deeply about the ones we love, and it hurts us to see them destroy themselves, but we must remember first and foremost that they have their own lives. We must be practical. If I were to have a son who smoked cigarettes, it would be pointless for me to continually lecture him about how his body is a temple of the Most High God, and that he commits a grave blasphemy every time he lights up. I must love him, invite him into my home, and wish to be with him, and support him in his life goals. I cannot directly support the smoking, although by supporting him I may indirectly support his sin. However, we are all sinners, and anytime we give anyone any sort of any kind, we may be indirectly supporting someone else’s sin.
As applied to your situation, you love your step-daughter. That is wonderful. Don’t alienate her. Homosexuality is wrong, but the only persons she is hurting is herself and those who willingly partake of her sin with her, as well as those she influences to be more open to the sin, but that is indirect on her part.
Hence, you can be a major part of your step-daughter’s life. However, her allowing you to be a part of it may mean that you have to tolerate the fact that she is a homosexual. She must never be allowed to believe for a second that you are okay with it, but she must also know that you love her and support her otherwise. Stay in her life, but if she never changes, I’m sorry, and that’s between her and God, but you have to love her and accept her.
Jesus told us to be perfect, and to those he healed and forgave he told, “Go and sin no more.” But he loved us while we were yet sinners.