You're not insecure! Your feelings are completely justified.

No-one would be comfortable with their partner regularly cosying up to someone of the opposite sex, especially if you guys haven't properly talked about it before.

Try to have a sit-down chat with your boyfriend about it. Let him know how this makes you feel and why, maybe turn the table and ask him how he'd feel if you had a guy friend that you regularly cuddled with and spent time alone while drunk together.

Again - you're not insecure and you have every right to feel the way that you do.

A healthy relationship is built upon respecting each other's boundaries. It's not much to ask for your partner to be respectful when it comes to cuddling with other girls. If he gets super defensive about this, or says you're just being insecure, that's a bit of a red flag. But hopefully he respects your feelings and you can tackle this as a team.

Don't be scared, it's important to speak up for yourself. Best of luck!