This is Dr. David
you could be having some excessive performance anxiety which can keeping you from being able ejaculate with penatrative sex.
you might also be use to masturbation to climax.
you can see a sex therapist about this. it would be best if you and your partner would go together.
there are exercises that you can do together to help improve sex and climax togethter.
you can show her how you masturbate during sex or foreplay and she can also masturbate you and give oral sex and see if this helps you climax.
sometime the type of condom you use can make a difference as well.
have you talked this over with your partner?
refraining from masturbating a few days before intercourse could help.
but to talk to partner about it.
it is an issue which affects both of you during sex. so best to talk about it.
not talking about it puts more pressure on you and more pressure and anxiety makes it harder for you to climax.
don't hid the fact that you masturbate from your partner.
you can show your partner how you masturbate during foreplay.
and show her how to pleasure you with her hand. and you can pleasure her with your hand as well.
this will bring the intimacy closer
and perhaps allow you to also climax better with her.
does this make sense?
do you have any other questions?
you will eventually be able to climax through intercouse with her
but you have to slowly move in that direction.
and take baby steps towards that.
you have been masturbating by yourself for a long time and this is what your body has been use to .
so you have to slowly transition to vaginal stimulation which is different from manual stimulation.