I feel horrible as it is please no judgement

My long time ex from forever ago dropped money that he owed me in my mailbox I just noticed it today when my friend noticed it and now my fiance is mad because I disrespected him when it was nothing to the situation he just wrote a note that said thanks. .. hes mad Because I shouldn't have contacted him when I didn't I have him blocked on everything he messaged my Facebook messages from a old old account that said it's here and my fiance thinks I did something like no I wouldn't cheat I was just helping him out forever ago he just now paid me back ...... I just now told my so about this because I just noticed it myself did I do something wrong or is he over reacting? I feel bad but I was just trying to help him out like I said it happened forever ago I actually forgot about it