I am from Pakistan and i have a residence card as an EU family member since I am married to a Greek woman with 2 children. I want to travel to London for 3 days with one friend of mine who is from an EU country but we are not family related. Is it possible to do so without a visa?
No. To enter the UK without a visa you need an Article 10 card and your EU family member must either be traveling with you or already in the UK:
If you are a non-EEA national who holds a valid genuine residence card, issued to you as the family member of an EEA national who is exercising free movement rights in another EEA State (i.e. not your EEA relative’s Member State of nationality) under Article 10 of Directive 2004/38/EC (the ‘Free Movement Directive’), you may use this document for travel to the UK if you are accompanying your EEA national relative here, or joining your EEA national relative in the UK.
You will need a standard visitor visa for this trip.