Threesomes in a relationship, opinions?

M

My partner keeps trying to convince me to have a threesome. Every time I even consider it for a few seconds, I imagine him sleeping with another woman and bawl my fucking eyes out. Yep. Maybe I'm a crybaby. Maybe it's because this man was my first kiss, my first love, took my virginity, and we have two beautiful children together... I don't know. Would you have a threesome with your partner?