Honestly, ideally a guy would last longer than that. But no man lasts an ideal amount of time! I've had sex plenty of times where it's gone on a while and I've ended up feeling a bit bored and have had to sort of pretend I'm enjoying it still out of politeness because I want the guy to get his. My first sexual partner didn't last that long but I never minded that much because we could just wait a bit and go again if we wanted. there was one time that he came literally as soon as he got inside, but we just laughed about it and it wasn't an issue at all. So in all I would prefer a guy to not last long enough than to last too long. Then at least she's enjoying everything that you do rather than waiting for it to finish.
The other thing is, you may find that you find you last longer during sex itself than during other stuff, particularly with condoms (and you can get ones that are slightly numbing which might help), and you will probably last longer with age as well. By the sounds of things you are good at the orgasms which is far far more important, anyway. I really can't imagine this issue being a dealbreaker at all, particularly if you are both as happy together as you imply. But communication is really important in a relationship so don't just bottle it up and let it come between you. As someone else said, it can be something you work on as a team.
Basically, I would suggest bringing her to orgasm before you have sex. Also, talk about it beforehand, mostly because then she will be able to reassure you and it won't be weighing on you so much (which I say not from a "it'll make it worse" point of view but simply because you should be able to enjoy sex with your girlfriend!).