Sexual problems

Amazingly I'm now in a relationship after a very long hiatus. Even more amazingly it seems to be working well, including the sex (which is lots - wow!).

Only one problem, I am not able to orgasm, at least not vaginally and only with extreme difficulty and much effort orally/manually (not always then either, most times it's just impossible; like I've managed it twice in more than 10 times that many 'episodes'). It's not like I'm not aroused, seem to be able to sustain an erection for hours, and I am super turned on, just can't seem to 'let go' and the harder I try the harder it gets (I have this problem with other things too like relaxing or swimming or heights).

I keep telling myself it's good that at least I'm not having performance problems, I am pleasing her very much it seems and very attentive (she says) and also I am well aware of tantra and the idea of orgasm not being the main goal - I am comfortable with that but she is not, she feels somehow that she isn't doing the right things to make me ejaculate and this is getting to her. I want her to feel good about herself and so want to be able to get there, even if for me it's really great despite that, any advice?