when he's home at weekends, do you live as husband and wife? From the socialising together etc it sounds as though you do (i.e. do you share food/the entire house etc). in which case, then there is no separation, as for 5 years separation to stand, it has to be complete separation, not just living apart Monday to Friday.
Its quite surprising that you are happy for the situation to go on as it has been for 10 years though. Are you not angry at your husband for using both you and this other woman for such a long time? Do you honestly believe that your marriage can be reconciled? If so, then perhaps its time to consider mediation. I wish you all the best with it.