Just stop wanking and looking at this crap on the internet! Seriously try and stop and see what you feel like after a month - hell you'll feel better after a couple of weeks!
It might be true that you've perhaps conditioned yourself to get turned on by these things, but it's just as possible to 'forget' what you've learnt too.
Also don't forget that when you're having sex for the first time it doesn't always go to plan and it's generally not that great - you're probably nervous and with all these doubts running through your head no wonder you lost your erection, you need to chill and just feel comfortable.
The fact you managed to get an erection and penetrate her shows that there is nothing wrong with you.
I'm making big assumptions here but if your spending ages on your computer wanking to this kind of thing, just switch off and go out and get some fresh air and meet some real people.
If you really need to beat off - try looking at other things like girl on girl action - you mention your love of tits - there's a whole world of awesome tit related porn out there.
If this girl is willing to take things slow that could be great as you can learn to explore each others bodies and get more comfortable with each other. Also another thing you could bear in mind, is to focusing on giving her an orgasm, stop worrying about what your body is doing or not doing and use you hands and mouth to make her explode.
You'll be fine, you just need to be strong and cut down (perhaps install a website nanny so you can't access porn so easily.)
Anyway that's the nice answer but in the spirit of this site - if you want an alternative we can always work something out where I buy you the biggest pair of implants and in return you can be my huge titted slut! :twisted: