Okay - step 1 - call a suicide hotline. It is confidential and trained people will assist you with next steps. If they talk you off the ledge (sorry, poor choice of words), then the next step is try to get into long-term therapy. If you are still going through crisis, then hospitalization is step-2. The hotline person can assist with referrals.
Now is not the time to feel embarrassed or ashamed. Do whatever you have to do to get therapists or counsellors in between you and your CTB desires. If you can share your struggles with your significant other, all the better. Sometimes going through these types of thoughts when you have others in your life but can't confide in them is more difficult than having no-one to turn to.
Do not give up and do not give in - you can do this. You made it this far.