Definition: Given a real-life anecdote of a complex ethical situation, generate a suitable title that describes the main event/root cause of the situation. Imagine that the given text is a social media post, and you have to write the title of the post, so the users can decide to read the main text or not.
Input: So my boyfriend and I have been together for over a year, both in our ealy 20s.
We're both very open about what we want and what we've done in the past, such as the fact I've had a few 3somes (ffm) which is what he wants with me. 
Normally I'd say yes and be excited, but I'm not particularly keen on doing this with him as I really do love him and I'm scared of the impact this may have on our relationship. I'm worried that after being with another woman he won't want me anymore, that I won't be "enough". 
He's never done anything to make me feel insecure, he's actually my first partner that's put an effort into telling me how much he loves me and attractive he finds me. I know if I tell him the reason why I don't want to he'll reassure me and tell me he'll always love me and my body and that he'll never leave me and that I'm enough. 
I feel like by saying no I'm not letting him fulfill his desire and that it's selfish of me to do that to him. 
AITA ? 

(Also, so sorry for the grammar.) 

not wanting a 3some