Is it ok for your fiance to sleep over at his ex wifes house?

2 weeks ago i found out my fiance took his ex wife and step child to a wrestling match 2 hrs away.he actually called me that night and acted like he was at his home getting ready to go to bed.what makes it worse is he slept over at her house! he said he got back at 2 am and didnt want to drive back home which is an hr away.well i live in the same town and am 10 min. away from her house he could of stayed at my house.he is saying they are just FRIENDS and not together. she even said i am acting like a 12yr old.by the way the only reason i found any of this out is because a friend of mine saw him at her house and i confronted him.we are still together after many apologies on his part but im refusing to wear my engagement ring and really reconsidering the whole relationship.they both say nothing happened and that i am being unreasonable and childish. am i?