Something new

So my one of my boyfriend's ex has contacted him asking if we would be interested in a threesome he said she has a high sex drive and could possibly teach me some things it would help improve our sex-life in general. I'm really shy when it comes to sex in general and I'm interested in learning some things but I've never done anything like this before and I'm nervous. What do you think? He's not pressuring me one way or another he told me it's up to me and if I say no he's okay with it.