I choose to differ from what your girlfriend feels because as much as penetrative sex is amazing, it is no match for cunnilingus; its not my opinion but some women who have experienced both penetrative sex as well as cunnilingus; 7 out of 10 times, they chose to go for cunnilingus because the orgasms just keep getting better and better. Its not common for a guy to stay hard for longer hours to be able to give the woman multiple orgasms, but with your fingers and your tongue, you could do just that.
When you engage in foreplay with your girlfriend, don’t merely see to that you both have a release, rather take time to enjoy and devour her body. Touch her like she has never been touched before. Spend more time playing her body if you want her to enjoy completely; the more time you play with her, the more satisfied she would be. Take her to new heights by touching her in a sensual and seductive way; let her beg you to go down on her.
Leave trails behind when you kiss her body, and when you’re ready to go down on her, don’t directly put your tongue on her vagina, rather kiss it gently, play with her inner thighs, kiss the sides of her vagina, lick it slowly and then when she asks you to lick her, do it. Go in a circular way by concentrating on her clit. The major work is finding her clit, once you do it, kiss it, suck it, play with it, and nibble with it; it would drive her mad. While you’re at it, gently insert your fingers one by one slowly and fuck her this way. I’m sure she would feel satisfied once you’re done with her by doing this.
Btw, its good that you’re preserving the penetrative part for after marriage, but what you’re doing falls pretty much under sex, so I see no reason why you should wait till your marriage while you’re doing everything other than penetration now. Good luck anyways.