Help!! I need non objective advice!!!!

My ex fiance last may we both decided to take a break.

I started talking to someone else and we decided to still go on our trip to florida 6 hours into the trip he asked what i had been up to? And i asked the same. he proceeded to tell me that he met someone at a wedding that i was suppose to attend and that he truly likes her! I told him the truth about meeting someone else. I left florida when i he got back home he took my car and gave it to his brother, who treated me badly, i caught his brother bad mouthing me 3 years earlier !!

After about a month i find out that he wants to get back together, so we did now we have been off and on! and i cannot stop thinking about what he did! and why he did not tell me in New york !! it has been about 1 year and i am not able to get over this !! what should i do! we constantly argue over this ! i have bitter feelings!!