You have the patience of a saint.

Your boyfriend gets distracted easily. You complain about this quality to one of your friends.

(someone) has the (something) of (something)

When you want to describe a person in a creative way, you can use a phrase like this:

You have the patience of a saint.

"You have the ___ of ___" means that the listener has the same amount of some quality as someone or something else. In this case, the speaker means that the listener is very patient, like a saint would be. Here are some other examples:

He has the strength of a lion.

You have the financial disciplne of a 19-year-old high school dropout

(someone's) attention span

A person's "attention span" is the length of time that they are able to focus on something.

I've always had a short attention span.

A person with a short attention span will quickly lose focus on what they're doing and start talking or thinking about something different instead. This is usually a negative quality.