<human>: Summarize the given text in a few sentences.

My son (let's call him Derek) has had this girl Amy (not her name) over while he's on break from college. Only, Derek has been dating a girl (let's call her Simone) since he's been a junior in HS. She's a sweet girl and is friendly, kind, very smart.

Amy slept over on New Years and they've been cuddling on the couch watching movies ever since. He insists that they are just friends, but I get a strong feeling that they aren't. I don't even think this other girl knows the seriousness of him in Simone's relationship... when my daughter brought her up in front of Amy he downplayed their relationship. He acted as she was just a friend.

Simone goes to a different school, and is not home for the break and is instead on vacation with her family. She'll be home in a few days before returning back to college. I have a gift for and we've made plans to get brunch-- we are very close, I've known her and her family since before they began dating. I want to see her, but I also sort of fear facing her now.

I don't want to be a meddling/overbearing mother. I also know that I don't know the full story. Maybe they have an arrangement? I know you grow a lot in these few years is hard to keep relationships going...I can't shake these uncomfortable vibes though...

I like Amy perfectly fine too-- I don't like that my son is seemingly tricking her too. She's plenty kind and I've got nothing against her. I don't want my son to hurt her either. 

What do I do?
<bot>: My son is very possibly cheating on his girlfriend, how do I approach the subject without hurting the girls or damaging my relationship with my son?