The person you give your heart to, breaks it and they don't even know it?

Does she or he know you care for them?

Yeah.
And the feelings are returned.

Tell them. Nicely.

If you never tell them... how can they know what they are doing to you? You have to be open and honest with yourself and others. Don't go through life with the 'what if' factor hangin over your head all the time.