mutual friends

I met my boyfriend through mutual friends.

If you have 'mutual friends', it means that you have some of the same friends or you share friends. Notice the following:

1. Working in the same business we have a lot of mutual friends.
   
2. My boyfriend and I don't have any mutual friends.
   

go on dates

Did you actually go on dates with him when you were 14?

When you 'go on dates', it means that you go out someplace romantically together, like a movie or dinner. Notice the following:

1. We used to go on dates a lot before we had kids.
   
2. Do you go on dates or just spend time together?
   

cool

Were your parents cool with you having a boyfriend?

If a person 'is cool' with something it means that it is okay with them or they permit it. Notice the following:

1. Is it cool if I come a little later?
   
2. My boss is really cool about most things.
   

keep in touch

Do you still keep in touch with him?

If you continue contact with someone it means that you 'keep in touch' with that person. Notice the following:

1. We keep in touch mostly through email now.
2. Are you good about keeping in touch with the people from back home?
   

flat

He's living in my flat at the moment.

A 'flat' is another name for apartment. Notice the following:

1. Do you share your flat with anyone?
   
2. You flat is decorated really well.