Why did 앤젤 leave the Buffy series so early?? What season should he really had left?

We all know the storyline behind why 앤젤 had to leave, but personally (rewatching season 5 currently) Riley Finn drives me nuts and I find myself wishing 앤젤 had never been written out so early!

Which Season would 당신 say 앤젤 should have stayed until, 또는 if not why not?

I do believe 앤젤 and Buffy should stay away from each other, but I also believe 앤젤 would have been interesting as a witness to spike's 사랑 for Buffy. Opinions?