I'm going to keep my fwb's number
How many times have you had sex in relationships?
Probably about 3 times, and twice was when I was dating someone.
You should move on and not keep contact with a fwb. If you keep seeing them over and over again, one of you is going to develop feelings for the other and will ruin the agreement you made.
How do you know that?
It seems that is what always happens , usually it is inevitable. It's wrong to get involved sexually with friends because it would just ruin everything that you have. You might meet someone later and really hurt their feelings.