My friend has started dating,

I don’t have a large amount of friends, most people I interact with are colleagues and the interaction is work based.

my social circle is made up of two ladies, both a similar age to me, one of them has been dating guys for as long as I can remember. I have never been over bothered by “boyfriends” that have come along and gone away. 
The second friend has recently started dating a guy and it has really effected me., so much so that I considering pulling away from her. 
Has  anyone else felt like this and how have you behaved in a situation such as this 

all thoughts are welcome.