Seems like your whole social life was dependent on your partner? Which tends to happen with men and is - in my and many others eyes- not healthy for a relationship. Invest in your social life, as you would in other aspects (work/health/fin), and start building.

The start up cost is vulnerability: if you meet someone you like to be friends with you need to essentially tell them 'I like you, I want to have you as my friend, I want to spend time with you, lets' hang'. The vulnerability and awkwardness are the initial price.