Are you taking any kind of medication? Like for pain or depressions, I had this problem too and I was on anti-depressants. It took the sensitivity down a lot, and felt like I could only get real pleasure out of oral, because with the condom I had little to no feeling.

Also are you able to get yourself off quicker than that? If you are still turned on by her, then it's probably not physchological..

OH! Are you holding back like at first when you are having sex, do you feel like you are going to come do you hold it back? When I do this it can sometimes make the sex turn from 30-40 min to an hour easy... Which is still good but like you said gets tiring after awhile.

Are you doing 2 hrs of sex? or does this include foreplay etc.
My b/f can usually last as long as I need him too... b/c it does sometimes take me a bit.

Yesterday I did what Doc always suggests of doing oral/foreplay until you are almost there and then start intercourse.
My b/f was doing oral on me, and I was giving him a handy... I can cum orally but it feels more intense during sex..but I rarely can in missionary unless I have some sort or clitoral stimulation.

I was soooo close during the oral.. I was like f*ck me! lol
so while he was getting into position for missionary... I just kept rubbing my clit...not letting the buildup get away.... he entered me and I came like under a minute...and I guess this all had him so worked up that he came shortly after LOL
It was nice not having to be pounded away for 5-10 minutes really working at it to make it happen... it just happened :)

> everything went better than expected, including the fact that it took me 25 minutes to cum. that wasnt bad at all but the problem was that everytime since its taken longer and longer. just yesterday we went at it for 2 HOURS and this time i didnt come simply because both of us were too tired to move.

Questions-
* What were the two of you doing for those 25 minutes?
* What were the two of you doing for those 2 HOURS?

Is the majority of your time devoted to making out including some foreplay before intercourse, or, are you spending most of this time stroking away in an attempt to build your arousal to the brink of a climax?

If the latter, you are placing the proverbial cart before the horse and going about this all wrong.

If the former, then follow what Sera did. Wait until you are at the brink of a climax to roll on the condom.

For more insight and information, please read the chapters in this Sticky Post:
INTERCOURSE / ORGASMS / and the gentle art of Humping

Since you just recently started having sex and you are still new to it, you shouldn't have problems already with not being able to cum. I agree with dancingdoc, were you doing something different in the 25 minutes during the first time than you were in the 2 hours of the next time? That might be your answer. If not, don't worry too much, you still have a lot of things to experiment with as far as toys, positions, oral, anal, etc. But, I would definitely try what demonbuttercup said, do whatever to get yourself to the point where you are almost about to cum, even if you have to use your own hand, and then put it in her. But if you can, try to get her to cum first because chances are if you cum before she does, you won't stay hard enough. Then not only will she think it's her fault when you don't cum, but she will be frustrated that she didn't either!