I want you to know that these intrusive thoughts you have been having, no matter how twisted you think they, are clearly not a part of who you want to be, and any therapist worth their salt will see that.
The first thing I recommend when you go in, is to straight up ask them if they have experience with OCD and intrusive thoughts. This way you know know straight away whether the therapist will understand your situation. It also supplies the therapist with context right from the beginning that these thoughts do not coincide with your intentions.
No matter how close you think you might have gotten to acting on these thoughts, you haven't, because it isn't what you really want. You have just built up this idea in your head that some part of you must actually want these intrusive thoughts to happen since you can't stop thinking about it, but I can %100 guarantee you that you don't. Someone who really wanted to commit these acts would not be seeking a therapist or asking for advice on reddit for how to get past them. They would be actively seeking out ways to make these thoughts reality and would not be experiencing the moral dilemma you are feeling right now.
You feel guilty for these thoughts you are having, despite the fact that they are clearly beyond your control. I think a therapist will help provide an outside perspective of how little these thoughts actually reflect who you are. They will also allow you to work your way through it at a pace you feel comfortable. They aren't there to get you in trouble, or pry out some deep dark secret, they are there to help you overcome these crippling thoughts.
You also don't have to say anything you don't want, and you don't have to tell them everything at once, but I can assure you that if they have any experience with OCD they have heard it before and will not see you any differently or hold it against you. They know that these thoughts aren't how you truly feel. Having that one person who you can be actually be open and honest with will be the biggest relief you have felt in a long time.
It is your best chance for finally overcoming these intrusive thoughts, and if you truly feel you are at risk of acting on these thoughts then you can't afford to not see a therapist. Again, you don't have to admit to all of your intrusive thoughts at once, but truly believe you will feel like a great weight has been lifted off your back when you can finally have an open conversation with someone other then yourself. I hope you do see a therapist and I hope you can find the help and relief you need. Good luck.