You can be a healthy vegetarian provided that you eat a balanced diet. No need to take supplements unless some crucial thing is missing from your diet (like @Seek_Kolinahr and soy products). Plenty of veggies and fruit is important.
Going back to meat-eating if you’ve been a vegetarian for a few years, should be done gradually, because as a vegetarian your digestive tract “flora” (bacteria) changes, and if you suddenly started eating meat again you would not be able to digest it so well.
I was vegetarian for about 7 years and when I went back to eating meat I started with fish only for a couple of months, and gradually re-introduced meat one or two meals a week to begin with. I still don’t eat a lot of meat even now (15 years on) and I still choose vegetarian options fairly frequently, but it’s a blessing not to have to study ingredients labels any more.