meaning of ne

I was wondering when I talked to a friend lately he would often use "ne" at the end of each sentence. He didn't do that before. What meaning does it have? Maybe it has a special meaning other than "is that so"?

it means "is it" or "isn't it", mostly feminine though. I use it sometimes though... rarely.

it means "is it" or "isn't it"

No, it doesn't. That's one possible way to translate it, which is sometimes correct but most often isn't.

He didn't do that before.

he may not have interest on the subjects you are speaking.

Basically the "meaning" of the sentence-final ね is "I'm telling you this but you already knew it". Saying simply 「いいお天気です。」to someone would sound weird (in a face-to-face conversation, at least...) because the person already knows the weather is fine, so they would be confused as to why you are saying this. 「いいお天気ですね。」makes it explicit that yes, you know that they know that the weather is fine, and are only saying this for small talk.

The opposite of ね, by the way, is よ, which means "I'm telling you this thing that you didn't know previously." So be careful with よ, because if it turns out that they actually knew it, they could either be offended ("Is this guy taking me for a fool? Of course I knew this!") or (most likely if you are a foreigner) think you are just bad at Japanese.

Was your friend speaking in maybe keigo or more polite speech when you first started talking to them, and now they are just being more casual?

Yeah I think so. By the way I'm a western girl and he's Japanese. At first he used also the "masu" form and recently started to use the shorter forms of words. Maybe it's a sign that we became good friends?

Basically the "meaning" of the sentence-final ね is "I'm telling you this but you already knew it". Saying simply 「いいお天気です。」to someone would sound weird (in a face-to-face conversation, at least...) because the person already knows the weather is fine, so they would be confused as to why you are saying this. 「いいお天気ですね。」makes it explicit that yes, you know that they know that the weather is fine, and are only saying this for small talk.

Which is a long way to say that 'ne' essentially translates to "is it" or "isn't it", in the sense that it's marking a rhetorical question or statement.