I am in agreement with Bill3. I believe that here the main issue is the following: “He has always told me he finds commitment scary and fears away from a serious relationship.”
I think you may already be at unease with the above statement and hence feel uncomfortable when he looks at other women.
And, no it is not okay nor it is a ‘man thing’ to flirt with other women unless you two are both in agreement with it.
I think your intuition is telling you the reality vs fantasy. Listen to your intuition and please do not ignore the red flags. When we are in love and want to make a relationship work, we tend to ignore the red flags and focus on the positive even if it does not necessarily represent the reality.