I hate to answer a question with it's complicated but...it's complicated. The biggest problem of course is that Christians are all over the place on how they interpret the Bible. I'll take your last question first. Most Bible believing Christians (those who accept the Bible as the final authority for all theology) say Jesus "fulfilled" OT law. So yes, all of the OT still matters but we don't have to keep kosher because Jesus. Vast over simplification but this is only one of many issues with using the few OT passages that address homosexuality. So take Duetoronomy 22:5, “A woman shall not wear a man's garment, nor shall a man put on a woman's cloak, for whoever does these things is an abomination to the Lord your God." Wow, super clear. How could any Christian argue with that? But keep reading that passage and you'll get the following "You shall not sow your vineyard with two kinds of seed, lest the whole yield be forfeited" and "You shall not wear cloth of wool and linen mixed together." How many Christians have you met later worried about either of these laws? Keep reading, just a few verses later you'll get to the command that if a man accuses his new wife of being a virgin and her parents can prove she is (blood stained sheets) he's gotta pay a big fine and isn't allowed to divorce her ever. If the parents can prove her virture she must be stoned to death. How many Christians are proposing that these days? And that's just one chapter. There are explicit injunctions against all kinds of things we don't bat an eyelash about today. Want an example from the New Testament? Matthew 19:9, " I tell you that anyone who divorces his wife, except for sexual immorality, and marries another woman commits adultery." Most Christians don't follow this either and will allow divorce for almost any reason even in church leadership.