All relationships at times enter into a stagnation mode (partners become complacent in the relationship, external stressors put a strain on it, one of the partners may become disillusioned that happiness and satisfaction are to be found elsewhere-the reasons can be many)
Infidelity is one sight that one of the partners is seeking something else out of the relationship. You've shared that you've been left behind when she's out with others. That too is another sign.
You were right not wanting to be in limbo as that is not fair to you.
Only the two of you could decide if things are over. If you still want to give the relationship a chance and she's willing, then couple's counseling is one option. Other options would be to have a talk and figure out what each one wants from the relationship and expects of the other. Try to see where she thinks the relationship would be let's say in 6 months, 1 year and it the next 5 years. You have already been together for quite some time yet, it is never late to find out what makes each one unhappy and unsettled.
If you do not trust her and feel that the spark and the future with ere gone for you (and have not interest in wasting energy without knowing what the outcome would be), then it is over for the relationship.
Breaking Up Blues: A Guide to Survival and Growth by Deni Cullington (Paperback - May 14, 2008)
Couple's Communication Made Easy - Audio CD (Jun 2007)