It may be non-exclusive but you are still committed (if it is who I am thinking of). The nice thing about non-exclusive relationships it that it allows more freedom within the commitment. Your SO is not your only source of "whatever" and therefore it is easier to give them time and space. But someday, if you are always there for them and they are sometimes there or sometimes not there for you, it will drain you and you will need to let go. If you can transition to the same level of commitment as they have, then things even out and it can keep going forever. It is the imbalance that is not healthy.