I know I've mentioned this before, ...

[Zoli]

Did I use the commas correctly in this text?

I know I've mentioned this before, but I really want you to know how much I value your support. You're a true friend, which is hard to come by these days

 

[jutfrank]

The second is important but you could easily not the use first. In fact, unless you want to make a special point of making a pause there, I suggest you leave it out.

 

[emsr2d2]

You forgot to end with a full stop.