Guys with low self-esteem... do you flirt with girls because...?

because you need an ego boost and you will flirt with anybody to see if they might flirt back? or, do you mainly or only just do the flirting with ones you like or could potentially like more than friends??? this guy has repeatedly said to me he has low self-esteem. he has flirted... how do i explain. i made the contact first i suppose and it was a little flirty/friendly on my part... and he responded flirty back. and another time, i asked a normal question. he responded attaching a picture of himself (a little flirty but innocent, nothing vulgar). then i went along with it with my words (again a little friendly/flirty) and his response was very playful and cute. i take it as flirty. i just wonder if this is normal.... or if i should be wary. he hasn't asked me out yet. then again, he did say he broke up with his ex and perhaps he's just not ready (i dont know). i want to be careful I'm not starting to like a player..... or someone that just wants to feed off my emotion and not actually want to date me. Sorry getting long! Thank you!!!