There is a group of people (friends) composed of virgins (yes, u heard me). One of them is gay, and a monster who eats virgins. The protagonist is also one of them who had a crush on this girl, also part of the group.
At the ending, they had sex, so that the monster can't eat the girl. Then they defeated the monster using a grenade, explodes inside the stomach. After that, I think the protagonist became gay too.
I can hardly remember this movie... We watched this as an experiment at elementary education.
Yes and no.
It could be Ken Russell's "Lair of the White Worm" from 1988. (Review at this site.)
What matches your description
"The monster who eats virgins."
The first candidate is a boy scout who the villainess has picked up while he was thumbing a ride in the rain, but she is forced to drown him in the tub, when the doorbell rings. The second candidate is the girlfriend of one of the heroes, who has a crush on the girl. And the heroes have to rescue her, before the monster eats her.
They defeat the monster at the end by using a hand grenade that the hero pulls out of his sporran. Then because the hospital sent him the wrong antidote, he may become a snake creature like the villainess, and then bites the other hero of the film.
What does not match you description.
The group being all virgins. The sister of the almost victim is not a virgin, as she had a boyfriend who was killed in a motorbike accident.
And the group does not have sex to prevent themselves from being eaten by the monster.
Tjhe cast includes Amanda Donohoe as the villainess, Hugh Grant and Peter Capaldi as the heroes, and Catherine Oxenberg and Sammi Davis as the heroines.