Hi there kiune, and thank you for your question. So the thing with syntribation is that it is indirect stimulation of your clitoris (in other words, squeezing your thighs together is applying pressure on the area around your clitoris/glans and therefore onto them as well and stimulating them), so you are actually feeling pleasure via stimulation of the clitoris already, just not by touching it directly.
Some people find that the direct contact with the clitoris too stimulating or not as pleasurable as indirect stimulation. Other forms of indirect stimulation with or without a partner include "grinding" (with a partner partially clothed or not), or an object like a pillow (some people also put a vibrator under the pillow), or stimulation of the area with hands but through underwear and/or applying pressure more generally on the area or on the area around the vulva, instead of right on the clitoris.
Similarly, many people with a clitoris, vulva and vagina find that penetration is not as pleasurable, so it is okay if penetration isn't your thing. Also, the pain can be connected to being tense, which if you are putting a lot of pressure on yourself to enjoy it/work out how to feel pleasure from it/hurry the process, is more likely to happen. Since it sounds like you are worried about not being able to have fulfilling sex life without being able to masturbate in a specific way (direct clitoral stimulation), this could be playing a part here.
It is important to keep in mind is that our most important sex organ is in fact our brain, and if we're feeling stressed or putting pressure on ourselves to work out what works for us ASAP, it actually can act counterintuitively finding that pleasure, as our brain is preoccupied with feeling stressed. Whilst it might be a bit hard right now, it is best try and be patient with yourself.
Taking the pressure off yourself might look like taking some time off trying to masturbate in this way (or at all), for a few days or however long you need, and doing things you enjoy and find recharge and relax you, and/or continuing to masturbate in ways that you enjoy, and explore how you can integrate this kind of indirect stimulation into sexual activity with your partner, if you're exploring having sex together.
How does this all sound to you? We're here to chat any of them through and to answer any further questions or curiosities you might have.