dealing with my crazy

My husband and I have a wonderful relationship. He is my best friend, we've been together for 8 years and the sex is still amazing and I love him.
However, I come from a long history of dealing with infidelity. He's never done anything like that or to make me doubt him but I struggle a lot with handling all the issues that arise in my head. 
His boss asked him (I saw the message) to drive his coworker down the road to her bus stop when they close together because she hasn't been making it and the next one doesn't come for another hour. My husband agreed and immediately texted me what was going on etc. and said he felt bad for her. 
In this scenario my gut is telling me nothing is wrong, I don't need to worry, I should be proud that he wouldn't let someone stand outside in the winter cold for an hour etc. but my head is going crazy with "what ifs" and scenarios. I fully trust my husband and I know deep down this has nothing to do with him.
Any advice on how to deal? When he comes home tonight will be the first time he's given her a ride and my crazy side wants to be mad at him when I know I shouldn't be.