DEAR ZZINA POWER:  MY girlfriend wants us to have a threesome with her friend.

The problem is I don’t fancy the friend, and I don’t feel comfortable with the idea.

I’m 20 and my girlfriend is 19.

This is my first serious relationship and I thought our sex life was great, so I don’t understand why my girlfriend wants to do this.

To me, it is off limits and will spoil things.

But if I say “no” will she get bored and leave me?

ZZINA POWER SAYS: You should never feel pressured to do anything that makes you feel uncomfortable.

Threesomes are tricky, even when both partners want them, and emotions invariably become involved.

Tell your girlfriend you aren’t interested.

If she’d like to spice things up, my support pack 50 Ways To Add Fun To Sex should help.