Abbey - Try not to be to worried about the trips out of town. He's sleeping with her, right? I know overnight is different - I wouldn't intentionally up my travel in your situation, but don't make a big deal out of it either.
He's liking being around you lately and will miss you more when you are gone, right? (I'd stay a bit awol, just send him some pics of you having an awesome time) She's going to slip up - the more time they spend together, the more likely it is that she'll be needy, put pressure on him, be annoying, take him for granted, become less exciting. Plus, if you want it to be over with her, he's going to have to be a big boy and keep it in his pants if you go out of town....might as well let him work on that now.
If you can, change something while you are gone so that you look different, more sparkly when you get back. Earrings or haircut (if you can squeeze on in) or put on makeup and a nice outfit to come back in. That car ride home or walk in the door is like a 1st date every time. He's (and you are) discovering who you are now.
Faith is, at one and the same time, absolutely necessary and altogether impossible. --Stanislaw Lem
