I have been there n done that , and you are going to get many and varied responses.
The rejection part can be the hardest to deal with as it leads to depression and a feeling of not be worth anything to anyone.
It takes some self anylization ( i dont have spell check so please bare with me ) you need to be aware of yourself , and most importantly confident in yourself that you are good person.
take this into consideration also, would you really want to spend months or years with someone who in the end does not really love you ? Or has a casual approach on the matter of " love/ and possibly sex ".
I would say be greatful that at the very least when you are put in this friend zone, that the person has admitted it to you, and doesnt have a cruel heart and uses you.
And guess what, now that you are in this zone, learn from it, you have an opprotunity to ask this person to be honest with you and to really be your friend, and help you develope your strengths and work on your weaknesses.
You will also need to develop good discerning skills, you do not want to leave yourself open to being used or pushed over. But do not be paranoid either !
And dont beat yourself up in this process, if you are not called to live a life in marrage, it doesnt have to be a bad thing, it means that you have opprotunity to share this love by helping others in so many ways that are greatly needed in this world.
But if you are certain you want to live your life in a wonderful Blessed Marrage and have a family, take your time in your search, ask these people who only want to be your friend to go on a practice date with you , it could be fun, ( just make sure it is a dutch date= you are not paying for everything !

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Develope relationship skills with these friends, it will lead you to be better able to handle a real loving relationship … and lets say these friends dont even want to help you on a practice date or at all…
then that means they are just not interested in you, it has nothing to do with you being a bad person, or weird, or what ever else you can think of, be thankful that they are not using you.
It means you are open for real friends who want you as a friend, value your friendship and want to see you happy, because you make them happy and you are making their world a better place to be in and they want the same for you.
Dont give up.