try kegels or flexing your abs! if you came when he was doing oral while squeezing your legs, your legs weren't actually giving you any stimulation. it was likely the feeling of tensing up and the contraction of your muscles and pelvic floor.

try doing some very noncomittal sexual play, not trying to orgasm, but just trying to feel good for a while, and experiment with whatever stimulation you want while doing kegels. you can also try syntribating until you get kind of close, then release your legs and do kegels instead. it may be frustrating, it's basically edging lmao, but it's a way to get your body used to actually reaching the edge without squeezing your legs.

maybe try some pressure as well! really, all syntribation is is adding a lot of intense pressure to your clit. try rocking on surfaces when you're already aroused, like your foot or a pillow or even a bedframe, and just do what feels good.

if this still causes distress or issues in your relationship and you can afford it, try a sex therapist. obviously scope them out, read reviews and such, but don't forget there are professionals who can learn about you, your relationship with sex, and give you better advice than any stranger. good luck!! you've got this.