Why is he prolonging out situationship?

I have been in a situationship for 16 months he recently told me we can get into a relationship sometime this month we already spend 4 days out the week together he has met my child we are planning on moving in together this month he tells me he loves me and recently has been talking about marriage and starting a family but I caught him a few times talking to other females last week I went through his phone and he asked his brother to text females for him on Instagram and he told me he was just being sarcastic and when I catch him talking to other females he just will tell me we aren’t together and not exclusive is he prolonging our situation because he’s not ready for a relationship or is he just not interested in me and using me
Why is he prolonging out situationship?
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