My (29F) ex fiance (36M) p!ssed on our son's bathmat...should I confront him or just ignore it and not let him use our restroom anymore?

Edit: so there has been some confusion due to bad wording on my part. The bathmat that he urinated on was inside the bath tub. It was one of those rubber mats with the suction cups to prevent baby from slipping and getting hurt.
I am on mobile so apologies for formatting/ spelling errors etc...
So just for some background my ex and I have been split for almost a year, he was manipulative emotionally abusive and cheating. Our son lives with me and his dad comes over 2-4 times a week for about an hour or two at a time to visit our 2 year old son.
Last sunday night 2yo pooped in the bath so I cleaned it. Ffw to tuesday, ex comes over, we have a slight disagreement, he asks to use the restroom right before leaving. I didnt use the restroom for a couple hours afterwards but everytime I did I could smell an odor like a dirty hampster cage...that night before I bathed my son I was adamant to find where the smell was coming from so I sniffed it out and discovered it was coming from the bathmat, and there was some discoloration (greenish areas on the blue mat) I pulled it up and sure enough it smelled like ****. Grown up ****. My son has peed on this mat many times and it has never smelled like this. If I hadn't washed the mat in a few months I could maybe see a build up and weird odor but I had just washed it two nights before. There is no way my son's urine smelled this strongly. It had to be his father.
I am livid. I cannot believe that he would **** on his own son's bathmat. I dont know how to deal with this childish vindictive person. What do I do? I know he will deny it and it will cause a fight if I try talking to him about it. If I don't allow him to use my bathroom that will probably also cause tension. I would say we will only meet in public places from now on but that doesnt always work out and I always end up being the one to blame for that. I appreciate any suggestions on how to deal with this ridiculous situation.
Tl;dr: vindictive baby daddy urinated on my son's bathmat after we had a disagreement. Any suggestions to deal with this childishness aplrectiated.


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