What does it mean when he sends shirtless pics and pics of him in his underwear? How should I proceed?

Okay i know the answer is obvious. But im still halfway baffled and dont know what to think of it. I (f21) have this friend (m18) that is also a cousin of my ex (of 5 years). Long story short, the relationship with my ex was abusive and just weird af. Whenever we hung out with his cousin, lets call him A, i was really happy because i couldnt help but smile when he was around. We had a good friendship before i broke it of with my ex, but now ( 3 months later) it escelated like a lot. To the point of us being in physical contact 1/3 of the time we spend together, we snap/text/call each other all of the time. The snaps were just random from the start, then i started sending pics of my face with filters (i like to mess around with that, i do it with so many of my girl friends i didn't think itd mean anything), then it escelated to him being shirtless in bed before sleep. But i thought it was just situational. Yesterday he sends me a pic of him in his underwear in which his bulge was clearly visible. And im not gonna lie, i liked it. I brushed it off and just replied to what he said because it was an internal joke of a sort, it wasn't just like "here's my crotch". After that, he sends another one. I didn't send one back, im not comfortabpe with that. I didn't take notice of it but i didn't imply that i was bothered. The first dilema here is his age and second is his relation to my ex. We also got drunk together yesterday. The eye contact was so intense i could melt. I know he wants me. And i know i want him. But damn is this okay to proceed and how should i even take the fact that he sent me a pic like that?
What does it mean when he sends shirtless pics and pics of him in his underwear? How should I proceed?
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