This is an annoying and upsetting problem for you both, I am sure. There is no doubt that if he is experiencing high stress
levels at work, this can affect his ability to orgasm and ejaculate. My suggestion is that he use masturbation
as a "rehearsal" for sex. If he can masturbate to orgasm/ejaculation successfully, then this may translate into better results as a couple in the bedroom. Also, he may be able to finish better with manual or oral sex
techniques than with vaginal intercourse. The vagina is sometimes not tight enough and not guided enough a stimulation to allow for a good excitement phase that plateaus prior to orgasm/ejaculation. There is no use engaging in intercourse for 45 minutes if he doesn't feel aroused to a reasonable plateau at any point. It's better for him to pull out at some point and for you to try to finish him off with your hands, mouth, or even both and see if this works better for him. Communication during the act is crucial. You should ask him what he wants/needs from you and he should feel free and easy expressing this to you. This communication will also help him overcome this issue. It's great that you aren't pressuring him to perform, because that would certainly make it worse. Relaxing is more useful, for both of you. Best of luck and I hope things improve soon.