You're dating someone who you enjoy and like but who you know there is no long term potential with. You know that they are looking for that (a LT relationship) but for you, for whatever reason, it's just not there. You like being with them. You enjoy spending time with them. Maybe, you even really like having sex with them. But this is not someone who you think you could be happy with "till death do us part". Should you continue to date that person or should you break-up immediately?