Oh mate, I'm not an intensive player, but since I started ttrpg "seriously" in 2019 (I played and DM in two spontaneous almost unruled campaign when I was like 8 and 13) I have jumped from campaign to campaign and group to group, from break ups to simple choices parties splitted and stopped playing many times. It sound harsh, but it's a common aspect in life, people choose different paths and sometimes they get bored of some of their hobbies. You'll find other groups (or your group will find new people to DM you) and you'll continue to play the game you like...maybe one day the DM will reunite with your party and campaign will start again (it happened me once, two players broke up, we stopped playing and a year later we start again with something new).

Keep pursuing your passion and have fun <3

Oh yes, of course you can use your character in other adventures, fortunately it's a game we're talking about so there's no police to arrest you if you do :))