How do I overcome psychological erectile dysfunction?

I believe my problem is psychological as I have no problem getting an erection while I am alone. My problem is being able to maintain an erection during intercourse with a partner. I am able to get an erection during foreplay or oral, but, when we try to have intercourse the erection goes away within just a few strokes. I have tried all 3 of the currently available medications and nothing seems to work. I do take a b/p med, but I have tried not taking that and did not seem to make any difference one way or another as to performance. I am mid-fifties, overweight, high blood pressure. I have few opportunities to be with a partner, and would like to be able to actually complete intercourse with a lady given the opportunity.