Why We Didn't Have Sex!

My girlfriend (no name will be given and I will refer to her as such during the story) and I found ourselves just chilling on her bed, lying side by side enjoying each others company one afternoon last week. We like to trace our fingers lightly over each others bodies, even when intentions aren't sexual. It feels great and is a nice way to bond. After a while of this she started to slip her fingers under the waistband of my underwear and lightly traced the top of my pubic area. I of course immediately reacted, my heart started beating out of my chest, my breathing quickened and my cock twitched in excitement. Next I feel her warmth breath on my ear as she whispers dirty things in my ear and starts to bite it. This usually drives me mad with desire and this time was no different. At this point I knew she wasn't teasing and we were going to have some hard, raunchy sex. Or were we? I turned into her, kissed her long and deep while lightly tugging the back of her hair. I soon found myself on top of her as we ground ourselves together. Our clothes then came off, piece by piece and yet all at once, our bodies now grinding naked together as we continue kissing each other. I move off to the side and continue to kiss her as my hand moves towards her shaved pussy. I run my middle finger down her lips 3 times as I gather enough wetness to penetrate her. I slip my middle finger in and pump it in and out, slowly curling my finger at the same time. I now take my lubed up finger and start to slowly rub her clit in circles. Her body immediately reacts, she arches her back and a moan of pleasure escapes her lips. I rub harder and faster focusing only on her clit and she continues to moan louder every second. I tug harder on her hair with my other hand and she shoves her face into my neck, trying not to cry out in pleasure as her flatmates are home. Her hips start bucking and I know its time. I rub her as hard and fast as I can as she squirms about, moaning into my neck as her orgasm hits her. As she calms down I run my finger up and down her slit and ease it into her vagina. She looks into my eyes and we kiss. At this stage I find myself only semi-erect and start to worry if its going to happen again. Will I actually be able to have intercourse? My girlfriend notices and starts to play with my cock. She then licks it from base to shaft and starts going down on me, which is is ridiculously good at by the way! Intense pleasure immediately envelopes my body and I am soon back to full mast. She then stops and reaches from her drawer, pulls out a condom and hands it to me. I proceed to open it and put it on. As we position ourselves to have intercourse I notice once again I only have a semi and am not hard enough to actually have sex... This is not the first time this has happened. I lie back down in frustration and pull off the condom. My girlfriend is amazing and very understanding and is nonplussed. She continues her earlier activity of giving me a blowjob. Soon I can barely handle the pleasure as she moves her mouth up and down while holding the base of my shaft. My hands start to clench her bed sheets, I start to squirm twisting side to side as my orgasm hits me my hips buck in the air as I shoot rope after rope of cum into her mouth which she swallowed. I didn't even know if she swallowed or not until then. We always like to have long, naked cuddle sessions after anything sexual and this time was no different as we drifted into dreamland together (Just for a nap though). If anyone knows anything about my problem please don't hesitate to comment! Thanks for reading xxx