<human>: Can you succinctly summarize the text in 1-3 sentences?

25M, 21F.  1.5 year relationship with lots of ups and downs.  
Sex is great but communication is lacking.  We've been on and off for the last 2-3 months.

I love her but the relationship just doesn't work.  Some days I feel she is the girl of my dreams and that we should stick it out, communicate and fix our problems.  Other days I recall past actions, issues and realize it may never be better (major issue from my side is that i see her as a compulsive liar and as a result I don't fully trust and respect her).  On the other hand she does treat me very well (much better than I treat her)

This is my first "real" relationship.  How do I know it's time to let go or to continue working on it?
<bot>: 25M, 21F, 1.5 years.  On and off.  How do I know it's time to let go or to continue working on it?