I've known guys who were annoyed if you could not keep up. It's unfortunate. But then again we all have our faults. I have mine...
If your BF is not happy having to slow down and "drag" you around when the two of you are cycling, he needs some attitude adjustment or have him go for a high intensity ride first, come back and pick you up and go for his cool down ride with you.
Just because you can run 5/6 times a week does not mean that you would have the same kind of conditioning on a bike. Mechanics of running and riding a bike is different. When I used to really ride and do incredible rides, my running was just the awful. I couldn't run a 10 minute mile.
If your BF wants you to buy a new bike, tell him to put his money where his mouth is and have him pitch in to buy you a new bike. It sounds like he wants to spend your money so have him spend his own and buy you a new bike.
As for big box store bike. NOT WORTH IT!! It will be crummier than the one you have.
REI does carry good bicycles for very reasonable price. And when you have found the one you like. Come back and ask us if you think its a good deal or not. Then you can decide whether to buy it or not. REI is big enough that they will have more of the same bike somewhere. Buy last years close out model to get a better price deal.
Enjoy spending your BF's money :D :p

