Bought a sex doll, I’m farrr from recovery, advice?

Hey,

I’ve had sex in the past however the fear of failure constantly gets in the way and it’s caused a break up

I’ve been trying these exercises and figured I’d try it out on a sex doll before anything and it’s really helped me get used to the feeling of a vagina without the anxiety and fear or failure

If I’m laying down I can cum with ease and don’t require any masturbation, but if I try doing it while standing up, I can’t keep it up, so I have to masturbate to get myself hard and then put it back in but it goes soft again

How do I fix this?