OK, so let's try and get this right!
You are now registered under the WRS. Accordingly you are not yet entitled to apply for a Residence Permit, until near the end of the one-year of that WRS registration. You will indeed want to do so because only by getting that Residence Permit will you be able to work in the UK without being WRS-registered, given that you are from an A8 country.
Your time spent in the UK before you became WRS registered? You were a student and, as you say, you were limited to 20-hours work per week, at least during term-time. That time in the UK on a student visa will not assist in you getting ILR (except under Long Residence concession, and you don't qualify for that).
My fiance is from Afghanistan, he is waiting for ILR (sent his documents on February, is it normal to wait this long?
On what basis has he made his application? Long Residence Concession? It can easily take a year or more to decide such applications, especially the 14-year variety.
What is the plan? After he has got his ILR the two of you will get married? And then after that you will apply for a spouse visa ... to expedite your own ILR.
In a couple of years i want to apply for British passport
Well first you need to get your ILR! On your facts, if then married to a British Citizen, you might possibly be able to apply for naturalisation immediately after the ILR ... otherwise you will need to wait for a further year. So very doubtful you will achieve British Citizenship "in a couple of years".