I don’t trust my son’s boyfriend :(

[Pennifer]

My son is 23, his 21 year old boyfriend moved in a year ago.
He has mental health issues and is obviously unhappy with how things are and I want to be supportive.
My son has shared with me that they are working through some issues. My son is obviously run down and struggling with this.
But just recently his boyfriend has started having the odd night clubbing where he doesn’t come back overnight.
He spends hours on the phone to another guy and seems in awe of his income and lifestyle.
My son mentioned that he didn’t feel comfortable with the length of the phone calls.
We asked my son if they had an open relationship and he said they didn’t.
But on one of the boyfriends phone calls that he was having whilst walking into our cul de sac and our windows were open I heard him say that they have an open relationship.
He sounds open, flirtatious and happy when he’s on the phone to this guy but sadly my son and he are having a lot of tense discussions and arguments and only seem happy when they are watching TV.
We are all booked to go away next week on holiday and now his boyfriend has said he doesn’t want to go because he’s too stressed.
This is the bit where I feel supremely uncomfortable as I don’t trust him to be in the house on his own for the week. I feel there is stuff going on that I don’t know about, maybe also he is not being transparent with my son it seems, the “flirting” with this other guy. I’m a real home person and the thought of leaving this person that I’ve grown to be really unsure of in the house doesn’t feel comfortable.
Ive put my head above the parapet and said “sorry no, I don’t feel comfortable with that” but now I feel awful - they obviously have things to work out and I’m making it more difficult, it feels like I said this could be his home and now I’ve changed my mind, it feels like I’m not being supportive to my son.
I feel pretty bad and wanted to share.

[MeowMeowPowerRangers]

I would be asking him to move out.

[pocketvenuss]

It's obvious what bf is up to. He and your ds have to sort themselves out but no way do you need to allow your home to be an open house to someone disrespecting your son and will soon most likely be an ex.

[MissyB1]

He’s cheating on your ds and isn’t even hiding it well!
Who knows who will be in your house whilst you are away. That guy needs to be shown the door.

[Pumpkindoodles]

You need to give him notice and ask him to move out. Your DS isn’t happy
this guy is cheating on him and your DS can’t get away without making this person homeless.
21 is in most cases, too young to basically welcome their partner into the family by having them live there and join you on holidays.

[Pennifer]

Thanks for your comments all. It’s really useful to get other opinions.

[VatofTea]

He has mental health issues, and his judgment is clearly impaired. It's possible this guy has some sort of emotional attachment issues, and the spark has gone from your son (as he is the replacement provider) and the lodger is getting the spark from someone else.

He is not your problem, protect your son.

You need to communicate to them, that your home is not available for someone who doesn't value it or your goodwill.

If you can't trust this lodger, home alone, then you need to give him notice.