Guys....why do you sometimes act indecisive when you meet a woman you really like?

Look men, please help me understand you. Now I know not all guys are like this, but I know some who are so please advise: What if you meet a woman you're really attracted to and you get friendly with her and then you realise that she too is attracted to you! This is where your 'fear' seems to start. Then you 'get together' you know have a kiss and a little bit more. She's NOT coming on too strong. You really like her but you kind of act evasive, avoid her a little bit even...try to keep it really casual even if she asks to meet you again, you can't give a direct answer. Please explain this! Are you afraid of love?