I didn't use google, I used my Bible and a greek dictionary.
You're absolutely correct context is very improtant, and epithumia means a longing(especially for what's forbiden) that longing can also refer to lust or desire.
Rom 7:7(as you pointed out), Gal 5:16 and Jas 1:14-15 are a few examples of when the word's used to describe lust.
However in I Thess 2:17, Phil 1:23, and Matt 13:17 the word's used to express a longing to do something, but not able too. In Thess. Paul talks about how he wants to come see the brethren, but is unable too, b/c Satan has blocked his way. In Philipians Paul wants to be with Christ but realizes it's better for him to stay with the believers, and in Matthew 13 Jesus tells how many prophets and righteuous people have longed to see what the disciples had seen, but they weren't able too.
When you read Luke 22
I don't think it makes since to say Jesus was "lusting" after the passover. He's using the word like it's used in I Thess, Phil, and Matt. he's expressing a longing to have the passover, but he's unable too.