Is he cheating?

So my boyfriend, of over two years, and I just moved across the country. We only have one car at the moment, we're in our early twenties, so sometimes he has to get a ride home from work when I can't pick him up or he doesn't have the car. The girl who gives him a ride home is our age but shes doing us a big favor so I never really thought anything of it until some of the girls that work at his office told me they suspect she has a crush on my boyfriend. She will take time out of her day to stop by and talk to him or go out of her way to walk by his place in the office, but according to them this is never reciprocated by him. I thought it was just a harmless little crush until a few nights ago I was doing our laundry and found a shirt I've never seen before. I asked him about it and he said she gave it to him. I studied the shirt closely and noticed it was a women's shirt. I instantly interrogated him about it, assuming the shirt was actually hers and she had left it here in our home. He was very convincing and told me it was a gift from her and he didn't know how to politely say no to the gift (he's quite shy and very sweet). He has never cheated before. He has always been very faithful the past two years even when we spent 6 months living on opposite sides of the country. Nothing in our relationship has changed. He shows no signs of cheating or detachment, I even snooped through his emails and text messages to make sure he wasn't doing anything suspicious (I know I was invading his privacy but I felt it was necessary in this situation). I want to trust him and know he's not cheating on me but this situation seems way too sketchy to just let it brush off my shoulders. I don't know if he is lying and actually is cheating or if this girl is just oddly obsessed with my boyfriend and is looking to steal him away from me. I can't think of any reason a girl would "buy" him a women's shirt (unless it really was an accident and she meant to buy a mens), would drive 20 minutes out of her way to take him home in the afternoon, and other women at the office would tell me that she acts like she has a huge crush on him. I don't want to be made a fool of and trust him when this is going on right under my nose. So please I would like to hear opinions on this, I'm desperate.

If the shirt was in the laundry then he must have worn it. Have you ever seen him wear it? Did you ask him to put it on and see if it fit him? Even if she did give it to him it is no reason for him to wear it. I would just tell him you do not feel comfortable with him accepting gifts from this woman. Tell him the talk at his office and let him know that it is effecting you. Tell him that if other people at your office were telling him things about a man who was giving you rides home from work that this would be an issue with him as well. You both may need to just work really hard to find him another ride to work. I have actually been in this situation before and it got worse as time went on and destroyed the relationship. The rumors got too loud for me to ignore and his lack of consideration towards my feelings about it were too weak. If true or untrue he still needs to know and to work understand how this is effecting you. And if other then the shirt incident and some office rumors there is nothing more that would cause you too worry then make sure to remember that.