Son overreacting to sisters bf

[Mummacake]

So the teens are aged 18(m) & 16(f) Daughter has her first bf who is a lovely lady. Very polite & well mannered.

My daughter was chatting to him on facetime about maths revision this afternoon when her brother burst in to her room and was unbelievably rude to this lad, calling him all sorts and cut off their call. He then proceeded to come downstairs and question me about whether I'd met this lad etc. it was awful.
Really controlling & abusive behaviour, particularly towards his sister. This is very worrying & not something I tolerate due to their dad, long out of the picture) being a complete controlling narcissist.
Daughter has called the lad and he says it's fine; it clearly isn't & my son has stormed out. I'm gutted as I brought them up to be better than that.
I'm not sure how best to handle this tbh. He's becoming increasingly difficult over a number of things recently so some words of wisdom are welcome from any of those who've been there.

He's never had a girlfriend.

His paternal side of the family clearly wouldn't welcome a gay person.

Just giving opinions on what could be causing his anger.

Maybe he wants a girlfriend but he can’t find one who is interested?! Some people don’t get their first girlfriend until that age or later

@cerisepanther73 you've completely hit the nail on the head. It's like he's a walking ball of frustration atm. His dad basically ignored him & then compared him to the older boy - made a proper mess of him too 😔
I tried to get him into martial arts but he wasn't interested, but he says he'd like to give boxing a go & that starts tomorrow.
He's quite taken aback that I've 'got on his case' about it - like it's acceptable!!!
He self sabotages at every opportunity and I've really tried to get him to look at things differently but I may as well talk to the wall. Generally, he is actually a decent young person but I can't have the behaviour I saw this afternoon & I will not be bullied in my own home.
He's a bright kid but so lazy and puts effort into nothing except gym. His brother is currently taking a year out but not doing much and heaven forbid the younger one actually outperforms him. It's quite a complex picture with the older one.
As for being gay, he isn't but that wouldn't matter to me at all if he was. I just wonder if he feels everyone is passing him by - sometimes he believes the bs, rather than concentrate on doing well for himself.
I genuinely appreciate all your responses.

No they wouldn't accept him if he was gay. They're horrifically bigoted but don't see that they are the problem.
He's not had a 'proper' gfriend yet but he isn't gay. He's a bit shy when it comes to asking girls out. Though he needs to lose the current attitude first.

Your son knows how the lads talk about girls
He would die rather than hear another lad talking that way about his sister.

This is exactly the issue - thank you.
He has settled down a bit now. Still doesn't like it but has apologised for being so awful. The behaviour was so unexpected but also totally unacceptable so he needs to moderate his behaviour & learn to control his emotions going forward. Thanks everyone for all your perspectives & I'll close the thread now.