I also used to get very jealous of my husband when we were first married. Its different when you are not married, you have more space and time for yourself when you are single. You should be very careful not to lead this person on and try to tell them how you feel about them so they know if they should continue with you or give up for the time being. its not fair to drag someones heart around and it sounds like that will be what they are doing to you if you don't let them know how you feel. Personally i think you are lovesick, i know because i felt this way before a few times but you can gt over it and sometimes we have to just let go.