What do you do when you are no sure if the person you with is not the right one?

I don't know how long you have been in this relationship, but it is completely unfair for one the make another feel as if they aren't as good as them. If you have been together a really long time and you want to make it work, then you must get this out in the open. If not you will feel miserable. If you have not been with them for very long, then I would say so long and keep in mind you can't find someone else if you are with someone at the time. So the only way is to be alone for a while. Plus this will build your self esteem.