Advice needed. Worried about my stepfather's interactions with my son.

Apologies for what is bound to end up being a long, rambling post. Using a throw away account for obvious reasons. For the past year or so I've been getting increasingly 'bad feelings' about my stepfather's interactions with my son. My son isn't quite two and not very verbal so it's not as if I can ask him questions (not that I'd know where to start!). Whereas I can't say anything my stepfather has done is something that would cause alarm to anybody else, I can't help but find him creepy.He's very physically affectionate towards my son; when visiting he frequently kisses and cuddles him and loves to have him sitting on his lap. These acts, which seem and are completely innocent coming from anybody else, always manage to get my guard up when my stepfather is the one doing it. Occasionally he will squeeze his bum but that's about the only thing I can put my finger on that could potentially be seen as 'crossing a line'. He also offers to take my son into his garden or upstairs so he can 'explore' whilst I'm talking with my mum. Again, I don't bat an eyelid when anybody else offers to do the same. I'd also like to point out it's not because he's male; my dad, my brother and all of the men in my husband's family are just as affectionate with him but that doesn't get any alarm bells ringing.Now for a bit of background. When I was a teenager, I found letters to my stepfather from his ex-wife, threatening to reveal that he had sexually assaulted teenage girls. Apparently his ex-wife had victims who were willing to testify against my stepfather. My mother had kept the letters. As far as I'm aware, nothing ever came of these accusations. My stepfather and his ex-wife had a very nasty divorce so there is the possibility that these were nothing more than lies meant to damage his reputation. However, a few months ago my sister-in-law disclosed that my mother doesn't allow my stepfather to be alone with my nephew (three years old). My sister-in-law didn't know why. I also find my stepfather's interactions with my nephew to be unsettling.I shared my concerns with my dad who has also informed me that when my stepfather and mother first became an item, he was warned by others to 'watch his children'. Nothing ever happened to me or my brother. My dad doesn't have any reason I can think of to lie; he divorced my mum over two decades ago. My husband has always described my stepfather as 'weird' and 'odd' and since having our child and sharing my concerns with him, my husband is adamant that my stepfather is not to be trusted.On one instance when he took my son upstairs to play (gone for about ten minutes), when he returned downstairs his fly was undone (which my mother pointed out). My son wasn't distressed if anyway but I'm not naive enough to conclude that this means nothing happened. Similarly, I also know it could be a completely innocent coincidence. The thought makes me sick regardless.I guess my question is, how on earth do I handle this? I don't allow my son to go off anywhere with my stepfather since that incident but I'm quickly running out of plausible reasons as to why. I can't see a way in which I could ask him to stop being physically affectionate towards my son whilst allowing others to do the same. At the same time though, I want to do everything possible to keep my child safe. The only silver lining is that we don't live close to my mum and stepfather so I only see them about once a fortnight.Any advice greatly appreciated. This could of course just be the ramblings of a paranoid, overprotective mum. via /r/Parenting https://ift.tt/2FsUuUI