OH wants me to experiment

My partner of 9 years has a real thing for lesbian sex, I know he watches girl on girl porn and I'm ok with that as I watch porn too so it's no big deal to me as long as it's not obsessive and doesn't stop him wanting sex with me, which so far it hasn't.

For years he's been dropping hints about wanting to see me with another girl but I always thought it was just a fantasy to help him get aroused. Now he's made it clear that it's something he really wants, says he can't stop thinking about it. He asked for it as a Xmas present and didn't get it, now he's asking for it again for his birthday next month.

I told him I have a real problem with the thought of him watching me with a girl because I'm such a jealous person I'd worry he's getting more turned on by her than me.

He then said he'd be happy enough if I just did it and told him about it. He said it's not quite the same thing but he'd still get off on the idea and what I tell him.

I still don't know if he's 100% serious, he says he is but I don't think he realises the full implications of what he's proposing. I think to him it's all a game and a fantasy fuelled by the porn he watches which I've seen and it's so unrealistic, I watch lesbian porn too but genuine amateur stuff which is much less glitzy and glamorous but so much sexier in my eyes, real women making love which is what I'd want if I was ever going to try it.

The truth is I've been bi curious all my life and I'd love to try it with another girl but I have several reservations, namely A) That I'd get hooked on it and not want straight sex anymore and B) That the reality would be hugely disappointing to my OH as it wouldn't be anything like what he imagines. The way I see it, if I did it there would be no point in then telling him about it and making it sound like the sort of stuff he masturbates to, because I know for a fact it wouldn't play out in the same way and I'm not good at making stuff up.

Anyone else been in this situation?